util/superiotool: Tell compiler to use C99 instead of ANSI C

Fails to build on musl libc as pci/types.h expects "POSIX types", which
are not implemented, instead of stdint.h when using pre-C99 versions.

Change-Id: Id1cf5bd72a0b4d76c87dc62c443d02df18ddd3fe
Signed-off-by: Nicholas Sudsgaard <devel@nsudsgaard.com>
Reviewed-on: https://review.coreboot.org/c/coreboot/+/77791
Reviewed-by: Paul Menzel <paulepanter@mailbox.org>
Reviewed-by: Felix Singer <service+coreboot-gerrit@felixsinger.de>
Tested-by: build bot (Jenkins) <no-reply@coreboot.org>
diff --git a/util/superiotool/Makefile b/util/superiotool/Makefile
index e6a2160..fe2a4cc 100644
--- a/util/superiotool/Makefile
+++ b/util/superiotool/Makefile
@@ -12,7 +12,7 @@
 VERSION := -D'SUPERIOTOOL_VERSION="$(shell git describe 2>/dev/null)"'
 
 CFLAGS += -O2 -Wall -Wstrict-prototypes -Wundef -Wstrict-aliasing \
-         -Werror-implicit-function-declaration -ansi -pedantic $(VERSION) \
+         -Werror-implicit-function-declaration -std=c99 -pedantic $(VERSION) \
          -Wno-variadic-macros -I $(TOP)/src/commonlib/bsd/include
 LDFLAGS += -lz
 
@@ -25,7 +25,7 @@
 endif
 ifeq ($(OS_ARCH), FreeBSD)
 CFLAGS = -O2 -Wall -Werror -Wstrict-prototypes -Wundef -Wstrict-aliasing \
-         -Werror-implicit-function-declaration -ansi $(VERSION) \
+         -Werror-implicit-function-declaration -std=c99 $(VERSION) \
          -I/usr/local/include
 LDFLAGS += -L/usr/local/lib
 LIBS = -lz