# Replaces a compiler option or switch `old' in `var' by `new'.
# If `old' is not in `var', appends `new' to `var'.
# Example: llvm_replace_compiler_option(CMAKE_CXX_FLAGS_RELEASE "-O3" "-O2")
# Replaces a compiler option or switch `old' in `var' by `new'.
# If `old' is not in `var', appends `new' to `var'.
# Example: llvm_replace_compiler_option(CMAKE_CXX_FLAGS_RELEASE "-O3" "-O2")