configure.ac: Only define HAVE_LLVM if LLVM is used

Make sure that HAVE_LLVM compiler define is only set if LLVM is
actually used.

Signed-off-by: Tobias Droste <tdroste@gmx.de>
v2 [Emil] fold within the existing conditional
Reviewed-by: Emil Velikov <emil.velikov@collabora.com>
1 file changed