[CMake][Fuchsia] Enable --build-id linker flag by default

[phosek]

Summary

This enables passing --build-id to linker by default.

[mcgrathr]

lgtm

clang/cmake/caches/Fuchsia-stage2.cmake

 # This file sets up a CMakeCache for the second stage of a Fuchsia toolchain
 # build.
 
 set(LLVM_TARGETS_TO_BUILD X86;ARM;AArch64 CACHE STRING "")
 
 set(PACKAGE_VENDOR Fuchsia CACHE STRING "")
 
 set(LLVM_INCLUDE_EXAMPLES OFF CACHE BOOL "")
 set(LLVM_INCLUDE_DOCS OFF CACHE BOOL "")
 set(LLVM_ENABLE_BACKTRACES OFF CACHE BOOL "")
 set(LLVM_ENABLE_PER_TARGET_RUNTIME_DIR ON CACHE BOOL "")
 set(LLVM_ENABLE_TERMINFO OFF CACHE BOOL "")
 set(LLVM_ENABLE_ZLIB ON CACHE BOOL "")
 set(LLVM_EXTERNALIZE_DEBUGINFO ON CACHE BOOL "")
 set(CLANG_PLUGIN_SUPPORT OFF CACHE BOOL "")
 
+set(ENABLE_LINKER_BUILD_ID ON CACHE BOOL "")
+
 set(LLVM_ENABLE_LTO ON CACHE BOOL "")
 if(NOT APPLE)
   set(LLVM_ENABLE_LLD ON CACHE BOOL "")
   set(CLANG_DEFAULT_LINKER lld CACHE STRING "")
   set(CLANG_DEFAULT_OBJCOPY llvm-objcopy CACHE STRING "")
 endif()
 set(CLANG_DEFAULT_CXX_STDLIB libc++ CACHE STRING "")
 set(CLANG_DEFAULT_RTLIB compiler-rt CACHE STRING "")