Issue 1:
Tried to compile rustc@9b9833299245cc1eac68b52169e9152d0f412d6b on my Windows 7 x64 (MSYS2) when it crashed. Crashed even after running make clean first. For the record, I tried to compile with RUSTFLAGS='-C codegen-units=8' set.

$ export RUSTFLAGS='-C codegen-units=8'
$ make RUST_BACKTRACE=1
cfg: build triple i686-w64-mingw32
cfg: host triples i686-w64-mingw32
cfg: target triples i686-w64-mingw32
cfg: host for i686-w64-mingw32 is i386
cfg: os for i686-w64-mingw32 is w64-mingw32
cfg: using CC=gcc (CFG_CC)
cfg: disabling valgrind due to its unreliability on this platform
cfg: no llnextgen found, omitting grammar-verification
cfg: disabling doc build (CFG_DISABLE_DOCS)
rustc: i686-w64-mingw32/stage0/bin/rustlib/i686-w64-mingw32/lib/librand
i686-w64-mingw32\stage0\bin\rustlib\i686-w64-mingw32\lib\rand-4e7c5e5c.1.o:(.rdata+0x2b0): multiple definition of `isaac::IsaacRng.Rng::next_u32::_MSG_FILE_LINE::h3a06d40217e7486bdMb'
i686-w64-mingw32\stage0\bin\rustlib\i686-w64-mingw32\lib\rand-4e7c5e5c.0.o:(.rdata+0x3f0): first defined here
i686-w64-mingw32\stage0\bin\rustlib\i686-w64-mingw32\lib\rand-4e7c5e5c.1.o:(.rdata+0x300): multiple definition of `isaac::Isaac64Rng.Rng::next_u64::_MSG_FILE_LINE::h3a06d40217e7486bwgc'
i686-w64-mingw32\stage0\bin\rustlib\i686-w64-mingw32\lib\rand-4e7c5e5c.0.o:(.rdata+0x440): first defined here
i686-w64-mingw32\stage0\bin\rustlib\i686-w64-mingw32\lib\rand-4e7c5e5c.2.o:(.rdata+0x170): multiple definition of `isaac::IsaacRng.Rng::next_u32::_MSG_FILE_LINE::h3a06d40217e7486bdMb'
i686-w64-mingw32\stage0\bin\rustlib\i686-w64-mingw32\lib\rand-4e7c5e5c.0.o:(.rdata+0x3f0): first defined here
i686-w64-mingw32\stage0\bin\rustlib\i686-w64-mingw32\lib\rand-4e7c5e5c.2.o:(.rdata+0x1c0): multiple definition of `isaac::Isaac64Rng.Rng::next_u64::_MSG_FILE_LINE::h3a06d40217e7486bwgc'
i686-w64-mingw32\stage0\bin\rustlib\i686-w64-mingw32\lib\rand-4e7c5e5c.0.o:(.rdata+0x440): first defined here
i686-w64-mingw32\stage0\bin\rustlib\i686-w64-mingw32\lib\rand-4e7c5e5c.3.o:(.rdata+0x110): multiple definition of `isaac::IsaacRng.Rng::next_u32::_MSG_FILE_LINE::h3a06d40217e7486bdMb'
i686-w64-mingw32\stage0\bin\rustlib\i686-w64-mingw32\lib\rand-4e7c5e5c.0.o:(.rdata+0x3f0): first defined here
i686-w64-mingw32\stage0\bin\rustlib\i686-w64-mingw32\lib\rand-4e7c5e5c.3.o:(.rdata+0x160): multiple definition of `isaac::Isaac64Rng.Rng::next_u64::_MSG_FILE_LINE::h3a06d40217e7486bwgc'
i686-w64-mingw32\stage0\bin\rustlib\i686-w64-mingw32\lib\rand-4e7c5e5c.0.o:(.rdata+0x440): first defined here
i686-w64-mingw32\stage0\bin\rustlib\i686-w64-mingw32\lib\rand-4e7c5e5c.4.o:(.rdata+0x2aa0): multiple definition of `isaac::IsaacRng.Rng::next_u32::_MSG_FILE_LINE::h3a06d40217e7486bdMb'
i686-w64-mingw32\stage0\bin\rustlib\i686-w64-mingw32\lib\rand-4e7c5e5c.0.o:(.rdata+0x3f0): first defined here
i686-w64-mingw32\stage0\bin\rustlib\i686-w64-mingw32\lib\rand-4e7c5e5c.4.o:(.rdata+0x3b10): multiple definition of `isaac::Isaac64Rng.Rng::next_u64::_MSG_FILE_LINE::h3a06d40217e7486bwgc'
i686-w64-mingw32\stage0\bin\rustlib\i686-w64-mingw32\lib\rand-4e7c5e5c.0.o:(.rdata+0x440): first defined here
i686-w64-mingw32\stage0\bin\rustlib\i686-w64-mingw32\lib\rand-4e7c5e5c.5.o:(.rdata+0x70): multiple definition of `isaac::IsaacRng.Rng::next_u32::_MSG_FILE_LINE::h3a06d40217e7486bdMb'
i686-w64-mingw32\stage0\bin\rustlib\i686-w64-mingw32\lib\rand-4e7c5e5c.0.o:(.rdata+0x3f0): first defined here
i686-w64-mingw32\stage0\bin\rustlib\i686-w64-mingw32\lib\rand-4e7c5e5c.5.o:(.rdata+0xc0): multiple definition of `isaac::Isaac64Rng.Rng::next_u64::_MSG_FILE_LINE::h3a06d40217e7486bwgc'
i686-w64-mingw32\stage0\bin\rustlib\i686-w64-mingw32\lib\rand-4e7c5e5c.0.o:(.rdata+0x440): first defined here
i686-w64-mingw32\stage0\bin\rustlib\i686-w64-mingw32\lib\rand-4e7c5e5c.6.o:(.rdata+0x70): multiple definition of `isaac::IsaacRng.Rng::next_u32::_MSG_FILE_LINE::h3a06d40217e7486bdMb'
i686-w64-mingw32\stage0\bin\rustlib\i686-w64-mingw32\lib\rand-4e7c5e5c.0.o:(.rdata+0x3f0): first defined here
i686-w64-mingw32\stage0\bin\rustlib\i686-w64-mingw32\lib\rand-4e7c5e5c.6.o:(.rdata+0xc0): multiple definition of `isaac::Isaac64Rng.Rng::next_u64::_MSG_FILE_LINE::h3a06d40217e7486bwgc'
i686-w64-mingw32\stage0\bin\rustlib\i686-w64-mingw32\lib\rand-4e7c5e5c.0.o:(.rdata+0x440): first defined here
i686-w64-mingw32\stage0\bin\rustlib\i686-w64-mingw32\lib\rand-4e7c5e5c.7.o:(.rdata+0x70): multiple definition of `isaac::IsaacRng.Rng::next_u32::_MSG_FILE_LINE::h3a06d40217e7486bdMb'
i686-w64-mingw32\stage0\bin\rustlib\i686-w64-mingw32\lib\rand-4e7c5e5c.0.o:(.rdata+0x3f0): first defined here
i686-w64-mingw32\stage0\bin\rustlib\i686-w64-mingw32\lib\rand-4e7c5e5c.7.o:(.rdata+0xc0): multiple definition of `isaac::Isaac64Rng.Rng::next_u64::_MSG_FILE_LINE::h3a06d40217e7486bwgc'
i686-w64-mingw32\stage0\bin\rustlib\i686-w64-mingw32\lib\rand-4e7c5e5c.0.o:(.rdata+0x440): first defined here
collect2.exe: error: ld returned 1 exit status
error: internal compiler error: unexpected failure
note: the compiler hit an unexpected failure path. this is a bug.
note: we would appreciate a bug report: http://doc.rust-lang.org/complement-bugreport.html
note: run with `RUST_BACKTRACE=1` for a backtrace
task 'rustc' failed at 'called `Result::unwrap()` on an `Err` value: couldn't rename path (file not found (OS Error 2: Das System kann die angegebene Datei nicht finden.
); from=i686-w64-mingw32\stage0\bin\rustlib\i686-w64-mingw32\lib\rand-4e7c5e5c.o.exe; to=i686-w64-mingw32\stage0\bin\rustlib\i686-w64-mingw32\lib\rand-4e7c5e5c.o)', C:\bot\slave\snap3-win-32\build\src\libcore\result.rs:808

stack backtrace:
1: 0x1e64dca - main
2: 0x1e7be1c - main
3: 0x1e7bbad - main
4: 0x1e7b9c5 - main
5: 0x1ecb31f - main
6: 0x432cd2 - main
7: 0x42fc69 - main
8: 0xd04e86 - main
9: 0x421d49 - main
10: 0xcb3de1 - main
11: 0xcaccfc - main
12: 0xd2df45 - main
13: 0xd2bea4 - main
14: 0x439e7e - main
15: 0x439dc6 - main
16: 0x1abe123 - main
17: 0x1e7b81c - main
18: 0x1e79dfe - main
19: 0x1abdf91 - main
20: 0x1e7b507 - main
21: 0x777e9f72 - RtlInitializeExceptionChain

/f/Dokumente/Coding/rust/rust-lang/mk/target.mk:166: recipe for target 'i686-w64-mingw32/stage0/bin/rustlib/i686-w64-mingw32/lib/stamp.rand' failed
make: *** [i686-w64-mingw32/stage0/bin/rustlib/i686-w64-mingw32/lib/stamp.rand] Error 101

Issue 2:
==> ./configure --prefix=/Users/andrewrynhard/develop/homebrew/Cellar/rust/HEAD --disable-rpath --enable-clang --release-channel=nightly
configure:
configure: note, user-provided CC looks like clang; CC=clang.
configure:
configure: CFG_USING_CLANG := 1
configure: error: bad CLANG version: 7.0.0, need >=3.0svn