Fix the naming of an LLVM tool in common/clang.conf

Probably was copied from the gcc equivalent.

Change-Id: I87e17314d8b24ae983b1fffd14535b9d7f616a1b
Reviewed-by: Oswald Buddenhagen <oswald.buddenhagen@theqtcompany.com>
Reviewed-by: Olivier Goffart (Woboq GmbH) <ogoffart@woboq.com>

mkspecs/common/clang.conf

@@ -40,5 +40,5 @@ QMAKE_LFLAGS_LTCG       = $$QMAKE_CFLAGS_LTCG
 
 # Wrapper tools that understand .o/.a files with LLVM bytecode instead of machine code
 QMAKE_AR_LTCG           = llvm-ar cqs
-QMAKE_NM_LTCG           = gcc-nm -P
+QMAKE_NM_LTCG           = llvm-nm -P
 QMAKE_RANLIB_LTCG       = true      # No need to run, since llvm-ar has "s"