[asan] Disable instrumentation for available_externally global with COFF (#81109)

For COFF, available_externally global will be instrumented because of
the lack of filtering, and will trigger the Verifier pass assertion and
crash the compilation. This patch will filter out the
available_externally global for COFF.

For non-COFF, `!G->hasExactDefinition()` in line 1954 will filter out
the available_externally globals.

There is a related bug reported in
https://bugs.llvm.org/show_bug.cgi?id=47950 /
https://github.com/llvm/llvm-project/issues/47294. I tried the
reproducer posted on the page and this will fix the problem.

Reproducer:
```
#include <locale>

void grouping_impl() {
  std::use_facet<std::numpunct<char>>(std::locale());
}

// clang -fsanitize=address -D_DLL -std=c++14 -c format.cc
```