Compiler crashes displaying error line when compiling .rc files

[brson]

When compiling a .rc file and there is an error in one of the .rs files. The compiler will crash when trying to use the codemap to display which line the error was on.

Example:

../src/lib/test.rs:82:23:82:52: error: unknown type in conversion:
rt: d76f:main:main:                   upcall fail 'Assertion end <= str::byte_len(s) failed', /media/src/rust-tinderbox/srcdir-snap-stage3-x86_64-unknown-linux-gnu/src/lib/str.rs:393

This is likely because it is trying to relate numbers in the codemap to bytes in the file, but the codemap treats all files in the compilation unit as if they were one giant file. So when it goes to look up line 5 in foo.rs it may (currently) end up looking for byte 17000.

[brson]

This functionality is temporarily disabled in e53cfb9 because it was messing with the windows build bot

[brson]

Long fixed.