By default llvm (and rustc) generate sse2 instructions on x84, but
we have users on old cpus without this extension, causing crashes
in the rust code. Pass a flag when building for win32 to prevent this.
Export and AC_SUBST RUSTFLAGS so it's available in the build.
This apparently wasn't hooked up before.
-Wno-psabi has not been necessary since we updated the build machines to Android NDK r8c three years ago in bug 826133.
-Wsometimes-initialized is not necessary because it is implicitly enabled by clang's -Wuninitialized, which is enable by -Wall.
-Wcast-align is very noisy and we apparently only enable it for gcc on 32-bit x86 builds?
-Wno-unused-local-typedef is no longer necessary. This is the clang flag; gcc's flag is -Wno-unused-local-typedefs, with an 's'. Suppressing gcc's warning was recently deemed unnecessary and WONTFIX'd in bug 1243604. Unsurprisingly, we no longer need it on clang either.
-Wrange-loop-analysis is no longer necessary because it is implicitly enabled by -Wloop-analysis, which is enabled by the previous commit.
