Add `--linker` option to pass flags to the linker
rustc: Suppress derived pattern-match-checking errors

typeck::check::_match wasn't suppressing derived errors properly.
Fixed it.
Adds '--print-link-args' that outputs linker arguments that would be used
core: Document core::path::GenericPath's trait methods
core: Use a better termination condition in os::mkdir_recursive

Instead of checking whether the parent is "." or "/", check the
number of components.

Also, more tests.
libstd: remove implicit copying of BigInt/BigUint
libstd: modify wrong shift width.

borrow = *elem << (uint::bits - n_bits);

The code above contains a bug that the value of the right operand of the shift operator exceeds the size of the left operand,
because sizeof(*elem) == 32, and 0 <= n_bits < 32 in 64bit architecture.

If `--opt-level` option is not given to rustc, the code above runs as if the right operand is `(uint::bits - n_bits) % 32`,
but if --opt-level is given, `borrow` is always zero.

I wonder why this bug is not catched in the libstd's testsuite (I try the `rustc --test --opt-level=2 bigint.rs` before fixing the bug,
but the unittest passes normally.)
core: Replace uses of 'drop' in task module with 'finally'. #5379
rustc: Change At to Managed and Uniq to Owned
test: Remove run-pass/too-much-recursion.rs

I don't understand how this is still passing on the bots. This condition
should trigger an abort now.
librustc: Fix pattern matching on cross crate newtype structs.
Add test for cross crate newtype struct in match pattern.
rustc / test: Fix error message
auto merge of #6107 : catamorphism/rust/mkdir_recursive, r=brson

r? @brson This hopefully addresses your concerns about the termination condition, and adds more tests. With a bonus documentation commit.
auto merge of #6108 : gifnksm/rust/bigint-shift-bug, r=brson

`std::bigint` contains the following code.
```rust
borrow = *elem << (uint::bits - n_bits);
```
The code above contains a bug that the value of the right operand of the shift operator exceeds the size of the left operand,
because sizeof(*elem) == 32, and 0 <= n_bits < 32 in 64bit architecture.

If `--opt-level` option is not given to rustc, the code above runs as if the right operand is `(uint::bits - n_bits) % 32`,
but if --opt-level is given, `borrow` is always zero.

I wonder why this bug is not catched in the libstd's testsuite (I try the `rustc --test --opt-level=2 bigint.rs` before fixing the bug,
but the unittest passes normally.)

This pull request also removes the implicit vector copies in `bigint.rs`.
Change flags to -Z print-link-args and --link-args
auto merge of #6121 : luqmana/rust/newtype-cc, r=graydon

#6086
char: fix unused import warning
iter: add a find function
deleted two tests intended to test RUST_CC_ZEAL, an apparently defunct flag for the cycle collector