of compiler parameters explicitly added by the build
specification. This macro replaces the cmake built-in
`add_definitions'.
Detects glibc and defines _GNU_SOURCE accordingly.
Resolves bug 3882.
git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@68428 91177308-0d34-0410-b5e6-96231b3b80d8