[toolchain][go][mac] Support use_strip on Mac
llvm-objcopy doesn't support stripping Mach-O binaries currently. Use `xcrun
strip` to strip for clang-gn-built and go-built binaries.
Note that -x is used for .so in the C++ toolchain, but no args for C++
executables (equivalent to -u -r per `man strip` and recommended there).
However, on Go 1.10, strip of an executable causes the resulting binary to
segfault, and on Go 1.11, strip without -x fails citing "symbols referenced by
indirect symbol table entries that can't be stripped". So for Go, always use
`strip -x`.
DX-555 #comment
Test: Manual
Change-Id: I40f54b0f1e1628562fa84893bc3b708dc9e2f5cd
2 files changed
