change value for CC on macOS (#167)

platforms/unix/Makefile

@@ -7,6 +7,8 @@
 
 .POSIX:
 
+UNAME := $(shell uname -s)
+
 # Options include: PF_SUPPORT_FP PF_NO_MALLOC PF_NO_INIT PF_DEBUG
 # See "docs/pf_ref.htm" file for more info.
 
@@ -45,6 +47,11 @@ IO_SOURCE = pf_io_posix.c pf_fileio_stdio.c
 
 EMBCCOPTS = -DPF_STATIC_DIC #-DPF_NO_FILEIO
 
+# c99 on macOS doesn't handle the command line options properly
+ifeq "$(UNAME)" "Darwin"
+	CC=clang
+endif
+
 #######################################
 PFINCLUDES = pf_all.h pf_cglue.h pf_clib.h pf_core.h pf_float.h \
 	pf_guts.h pf_host.h pf_inc1.h pf_io.h pf_mem.h pf_save.h \