Revert "[cmake] Disable GCC lifetime DSE"

This reverts commit ce990b5.

This breaks some build bots - specifically when using GCC to build LLVM and
then -fno-lifetime-dse ends up passed to Clang in some tests like at
https://lab.llvm.org/buildbot/#/builders/139/builds/40594.

Bug: #24952
Bug: #57740

Differential Revision: https://reviews.llvm.org/D150505

llvm/cmake/modules/HandleLLVMOptions.cmake

@@ -594,16 +594,6 @@ if ( LLVM_COMPILER_IS_GCC_COMPATIBLE OR CMAKE_CXX_COMPILER_ID MATCHES "XL" )
   add_flag_if_supported("-Werror=unguarded-availability-new" WERROR_UNGUARDED_AVAILABILITY_NEW)
 endif( LLVM_COMPILER_IS_GCC_COMPATIBLE OR CMAKE_CXX_COMPILER_ID MATCHES "XL" )
 
-if ( LLVM_COMPILER_IS_GCC_COMPATIBLE )
-  # 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
-  # crash if LLVM is built with GCC and LTO enabled (#57740).  Until
-  # these bugs are fixed, we need to disable dead store eliminations
-  # based on object lifetime.
-  add_flag_if_supported("-fno-lifetime-dse" CMAKE_CXX_FLAGS)
-endif ( LLVM_COMPILER_IS_GCC_COMPATIBLE )
-
 # Modules enablement for GCC-compatible compilers:
 if ( LLVM_COMPILER_IS_GCC_COMPATIBLE AND LLVM_ENABLE_MODULES )
   set(OLD_CMAKE_REQUIRED_FLAGS ${CMAKE_REQUIRED_FLAGS})