Revert "Add -fno-builtin to the tests as well."

This reverts commit f7a18b519dc6ba654fce73fdfb554d7781c18733.

test/Makefile

@@ -12,10 +12,10 @@ all: test-double test-float # test-double-system test-float-system
 bench: bench-syslibm bench-openlibm
 
 test-double: test-double.c libm-test.c
-	$(CC) $(CPPFLAGS) $(CFLAGS) -fno-builtin $(CFLAGS_add_TARGET_$(ARCH)) $(LDFLAGS) [email protected] -D__BSD_VISIBLE -I ../include -I../src $(OPENLIBM_LIB) -o $@
+	$(CC) $(CPPFLAGS) $(CFLAGS) $(CFLAGS_add_TARGET_$(ARCH)) $(LDFLAGS) [email protected] -D__BSD_VISIBLE -I ../include -I../src $(OPENLIBM_LIB) -o $@
 
 test-float: test-float.c libm-test.c
-	$(CC) $(CPPFLAGS) $(CFLAGS) -fno-builtin $(CFLAGS_add_TARGET_$(ARCH)) $(LDFLAGS) [email protected] -D__BSD_VISIBLE -I ../include -I../src $(OPENLIBM_LIB) -o $@
+	$(CC) $(CPPFLAGS) $(CFLAGS) $(CFLAGS_add_TARGET_$(ARCH)) $(LDFLAGS) [email protected] -D__BSD_VISIBLE -I ../include -I../src $(OPENLIBM_LIB) -o $@
 
 test-double-system: test-double.c libm-test.c
 	$(CC) $(CPPFLAGS) $(CFLAGS) $(CFLAGS_add_TARGET_$(ARCH)) $(LDFLAGS) $< -DSYS_MATH_H -lm -o $@