[dev.boringcrypto] cmd/go: exclude SysoFiles when using -msan
There's no way for a *.syso file to be compiled to work both in
normal mode and in msan mode. Assume they are compiled in
normal mode and drop them in msan mode.
Packages with syso files currently fail in -msan mode because
the syso file calls out to a routine like memcmp which then
falsely reports uninitialized memory. After this CL, they will fail
in -msan with link errors, because the syso will not be used.
But then it will at least be possible for package authors to write
fallback code in the package that avoids the syso in -msan mode,
so that the package with the syso can at least run in both modes.
Without this CL, that's not possible.
See #21884.
Change-Id: I77340614c4711325032484e65fa9c3f8332741d5
Reviewed-on: https://go-review.googlesource.com/63917 Reviewed-by: Adam Langley <agl@golang.org> Reviewed-by: Ian Lance Taylor <iant@golang.org>