gn build: Stop defining LLVM_ON_UNIX globally.

This macro is already being defined in llvm-config.h.

Differential Revision: https://reviews.llvm.org/D56626

llvm-svn: 351154

llvm/utils/gn/build/BUILD.gn

@@ -5,11 +5,6 @@ import("//llvm/utils/gn/build/toolchain/compiler.gni")
 config("compiler_defaults") {
   defines = []
 
-  # FIXME: Don't define this globally here.
-  if (host_os != "win") {
-    defines += [ "LLVM_ON_UNIX" ]
-  }
-
   if (!llvm_enable_assertions) {
     defines += [ "NDEBUG" ]
   }