crda: Makefile: fix .so compilation line with some compilers

Write the CC rule such that it only tries to produce a single output
file (the .so). When including the .h files in the compiler invocation,
this suggests we should be producing pre-compiled headers too, which
doesn't make sense in this context, and Clang happens not to like.

Signed-off-by: Brian Norris <briannorris@chromium.org>
Signed-off-by: Luis Chamberlain <mcgrof@kernel.org>

Makefile

diff --git a/Makefile b/Makefile
index 6169b1f..6ca26f3 100644
--- a/Makefile
+++ b/Makefile
@@ -114,9 +114,9 @@
 	$(NQ) '  Trusted pubkeys:' $(wildcard $(PUBKEY_DIR)/*.pem)
 	$(Q)./utils/key2pub.py --$* $(wildcard $(PUBKEY_DIR)/*.pem) $@
 
-$(LIBREG): regdb.h reglib.h reglib.c
+$(LIBREG): reglib.c regdb.h reglib.h
 	$(NQ) '  CC  ' $@
-	$(Q)$(CC) $(CFLAGS) $(CPPFLAGS) -o $@ -shared -Wl,-soname,$(LIBREG) $^
+	$(Q)$(CC) $(CFLAGS) $(CPPFLAGS) -o $@ -shared -Wl,-soname,$(LIBREG) $<
 
 install-libreg-headers:
 	$(NQ) '  INSTALL  libreg-headers'