Prevent generation of dependency on _cxa_guard for static initialization

This fixes an issue introduced by https://reviews.llvm.org/D70662

Function-scope static initialization are guarded in C++, so we should probably
not use it because it introduces a dependency on __cxa_guard* symbols.
In the context of clang, libasan is linked statically, and it currently needs to
the odd situation where compiling C code with clang and asan requires -lstdc++

Differential Revision: https://reviews.llvm.org/D102475

(cherry picked from commit 4144827)

Author: serge-sans-paille

compiler-rt/lib/sanitizer_common/sanitizer_posix_libcdep.cpp

@@ -166,9 +166,10 @@ bool SupportsColoredOutput(fd_t fd) {
 #if !SANITIZER_GO
 // TODO(glider): different tools may require different altstack size.
 static uptr GetAltStackSize() {
-  // SIGSTKSZ is not enough.
-  static const uptr kAltStackSize = SIGSTKSZ * 4;
-  return kAltStackSize;
+  // Note: since GLIBC_2.31, SIGSTKSZ may be a function call, so this may be
+  // more costly that you think. However GetAltStackSize is only call 2-3 times
+  // per thread so don't cache the evaluation.
+  return SIGSTKSZ * 4;
 }
 
 void SetAlternateSignalStack() {