Issue 1:
The problem occurs under OpenBSD (x86_64-unknown-openbsd).

The building of f174bca fail with SIGBUS, when compiling libstd using stage1/rustc. The last known to work build was ba2efe9 (~10 commits before).

Here the backtrace under gdb:

GNU gdb 6.3
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This GDB was configured as "amd64-unknown-openbsd5.7"...(no debugging symbols found)

(gdb) r
Starting program: /root/build/openbsd-master/build/x86_64-unknown-openbsd/stage1/bin/rustc --cfg stage1 -Z print-link-args -O --cfg rtopt --cfg debug --sysroot x86_64-unknown-openbsd/stage1 -C prefer-dynamic --target=x86_64-unknown-openbsd -D warnings -L x86_64-unknown-openbsd/rt -L /opt/llvm-32c27dda3ae2318b6897f00795009cd6f42ac4b3/lib -L '' --out-dir x86_64-unknown-openbsd/stage1/lib/rustlib/x86_64-unknown-openbsd/lib -C extra-filename=-4e7c5e5c /root/build/openbsd-master/src/libcore/lib.rs

Program received signal SIGBUS, Bus error.
[Switching to thread 1002137]
0x000005d798729cf0 in iter::FlatMap$LT$I$C$$u{20}U$C$$u{20}F$GT$.Iterator::next::h6743774523963745181 ()
from /root/build/openbsd-master/build/x86_64-unknown-openbsd/stage1/lib/librustc_driver-4e7c5e5c.so
(gdb) bt
#0 0x000005d798729cf0 in iter::FlatMap$LT$I$C$$u{20}U$C$$u{20}F$GT$.Iterator::next::h6743774523963745181 ()
from /root/build/openbsd-master/build/x86_64-unknown-openbsd/stage1/lib/librustc_driver-4e7c5e5c.so
#1 0x000005d79871593b in fold::noop_fold_item::h10734865051070155566 ()
from /root/build/openbsd-master/build/x86_64-unknown-openbsd/stage1/lib/librustc_driver-4e7c5e5c.so
#2 0x000005d798728157 in iter::FlatMap$LT$I$C$$u{20}U$C$$u{20}F$GT$.Iterator::next::closure.20907 ()
from /root/build/openbsd-master/build/x86_64-unknown-openbsd/stage1/lib/librustc_driver-4e7c5e5c.so
#3 0x000005d798727f0d in iter::FlatMap$LT$I$C$$u{20}U$C$$u{20}F$GT$.Iterator::next::h17973506744433351220 ()
from /root/build/openbsd-master/build/x86_64-unknown-openbsd/stage1/lib/librustc_driver-4e7c5e5c.so
#4 0x000005d798727298 in vec::Vec$LT$T$GT$.FromIterator$LT$T$GT$::from_iter::h11853285780444493736 ()
from /root/build/openbsd-master/build/x86_64-unknown-openbsd/stage1/lib/librustc_driver-4e7c5e5c.so
#5 0x000005d79871376c in fold::noop_fold_item::h10734865051070155566 ()
from /root/build/openbsd-master/build/x86_64-unknown-openbsd/stage1/lib/librustc_driver-4e7c5e5c.so
#6 0x000005d798728157 in iter::FlatMap$LT$I$C$$u{20}U$C$$u{20}F$GT$.Iterator::next::closure.20907 ()
from /root/build/openbsd-master/build/x86_64-unknown-openbsd/stage1/lib/librustc_driver-4e7c5e5c.so
#7 0x000005d798727f0d in iter::FlatMap$LT$I$C$$u{20}U$C$$u{20}F$GT$.Iterator::next::h17973506744433351220 ()
from /root/build/openbsd-master/build/x86_64-unknown-openbsd/stage1/lib/librustc_driver-4e7c5e5c.so
#8 0x000005d798727298 in vec::Vec$LT$T$GT$.FromIterator$LT$T$GT$::from_iter::h11853285780444493736 ()
from /root/build/openbsd-master/build/x86_64-unknown-openbsd/stage1/lib/librustc_driver-4e7c5e5c.so
#9 0x000005d79871376c in fold::noop_fold_item::h10734865051070155566 ()
from /root/build/openbsd-master/build/x86_64-unknown-openbsd/stage1/lib/librustc_driver-4e7c5e5c.so
#10 0x000005d7987109d5 in driver::assign_node_ids_and_map::closure.20285 ()
from /root/build/openbsd-master/build/x86_64-unknown-openbsd/stage1/lib/librustc_driver-4e7c5e5c.so
#11 0x000005d7986ce543 in driver::assign_node_ids_and_map::h6bc19e47b471dcd8hDa ()
from /root/build/openbsd-master/build/x86_64-unknown-openbsd/stage1/lib/librustc_driver-4e7c5e5c.so
#12 0x000005d7986be7c1 in driver::compile_input::h8dcb5e309d83154fEba ()
from /root/build/openbsd-master/build/x86_64-unknown-openbsd/stage1/lib/librustc_driver-4e7c5e5c.so
#13 0x000005d79876e26f in run_compiler::h0831f82d312bd846jbc ()
from /root/build/openbsd-master/build/x86_64-unknown-openbsd/stage1/lib/librustc_driver-4e7c5e5c.so
#14 0x000005d79876bd21 in thunk::F.Invoke$LT$A$C$$u{20}R$GT$::invoke::h15181002208922494184 ()
from /root/build/openbsd-master/build/x86_64-unknown-openbsd/stage1/lib/librustc_driver-4e7c5e5c.so
#15 0x000005d79876b042 in rt::unwind::try::try_fn::h10368191240528705449 ()
from /root/build/openbsd-master/build/x86_64-unknown-openbsd/stage1/lib/librustc_driver-4e7c5e5c.so
#16 0x000005d7dcbf35a9 in rust_try_inner () from /root/build/openbsd-master/build/x86_64-unknown-openbsd/stage1/lib/libstd-4e7c5e5c.so
#17 0x000005d7dcbf3596 in rust_try () from /root/build/openbsd-master/build/x86_64-unknown-openbsd/stage1/lib/libstd-4e7c5e5c.so
#18 0x000005d79876b61f in thunk::F.Invoke$LT$A$C$$u{20}R$GT$::invoke::h12343021353288682298 ()
from /root/build/openbsd-master/build/x86_64-unknown-openbsd/stage1/lib/librustc_driver-4e7c5e5c.so
#19 0x000005d7dcbb00ce in sys::thread::thread_start::hd53a9aab8f83598fqHE ()
from /root/build/openbsd-master/build/x86_64-unknown-openbsd/stage1/lib/libstd-4e7c5e5c.so
#20 0x000005d71b0e898e in _rthread_start (v=Variable "v" is not available.
) at /usr/src/lib/librthread/rthread.c:145
#21 0x000005d7eb2c059b in __tfork_thread () at /usr/src/lib/libc/arch/amd64/sys/tfork_thread.S:75
#22 0x0000000000000000 in ?? ()
(gdb)

The builds are without jemalloc.

Issue 2:
Configuring with ../configure --disable-docs --enable-ccache --disable-jemalloc causes the build to fail with:

x86_64-unknown-linux-gnu/stage1/lib/rustlib/x86_64-unknown-linux-gnu/lib/libcore
Illegal instruction (core dumped)

Usually it is Illegal instruction however sometimes a bad or double free is reported.

Building with jemalloc enabled (../configure --disable-docs --enable-ccache) has no problem.