[cmake] Fix -fno-lifetime-dse not being passed to GCC

A follow-up to #92953. This should fix unexpected performance gains when Clang is built with GCC, and fix downstream LTO crashes reported in 4feae05#r142466703

Author: Endilll

llvm/cmake/modules/HandleLLVMOptions.cmake

@@ -672,7 +672,7 @@ if (CMAKE_CXX_COMPILER_ID MATCHES "Clang")
   append("-Werror=unguarded-availability-new" CMAKE_C_FLAGS CMAKE_CXX_FLAGS)
 endif()
 
-if (CMAKE_CXX_COMPILER_ID STREQUAL "GCC")
+if (CMAKE_CXX_COMPILER_ID STREQUAL "GNU")
   # LLVM data structures like llvm::User and llvm::MDNode rely on
   # the value of object storage persisting beyond the lifetime of the
   # object (#24952).  This is not standard compliant and causes a runtime