[Fuchsia] Include llvm-gsymutil tool in the Fuchsia toolchain

This tool is used for generating and manipulating GSYM files.

Differential Revision: https://reviews.llvm.org/D76204

Author: petrhosek

clang/cmake/caches/Fuchsia-stage2.cmake

@@ -195,6 +195,7 @@ set(LLVM_TOOLCHAIN_TOOLS
   llvm-cxxfilt
   llvm-dwarfdump
   llvm-dwp
+  llvm-gsymutil
   llvm-lib
   llvm-nm
   llvm-objcopy