configure: separate callisto's cppflags from other libraries' cppflags

configure

@@ -7,7 +7,8 @@ set -e
 mkf=config.mk
 # these also apply to all libraries in external/
 cflags='-std=c99'
-cppflags='-DLUA_USE_POSIX'
+cppflags=''
+ext_cppflags='-DLUA_USE_POSIX'
 ldflags='-lm'
 # optional libraries to build with support for; a dynamically
 # linked Lua 5.4 library may be supported here later
@@ -203,9 +204,12 @@ _CC       = %s
 _CFLAGS   = %s
 _CPPFLAGS = %s
 _LDFLAGS  =%s
+
+_EXT_CPPFLAGS = %s
 '              \
 	"$cc"      \
 	"$cflags"  \
 	"$cppflags"\
 	"$ldflags" \
+	"$ext_cppflags"\
 		>"$mkf"

external/lua/Makefile

@@ -6,7 +6,7 @@
 include ../../config.mk
 
 CC=      ${_CC}
-CFLAGS=  ${_CFLAGS} ${_CPPFLAGS}
+CFLAGS=  ${_CFLAGS} ${_EXT_CPPFLAGS}
 LDFLAGS= ${_LDFLAGS}
 
 AR= ar cr

external/lua/patches/lua-5.4.6-makefile.diff

@@ -13,7 +13,7 @@
 -LDFLAGS= $(SYSLDFLAGS) $(MYLDFLAGS)
 -LIBS= -lm $(SYSLIBS) $(MYLIBS)
 +CC=      ${_CC}
-+CFLAGS=  ${_CFLAGS} ${_CPPFLAGS}
++CFLAGS=  ${_CFLAGS} ${_EXT_CPPFLAGS}
 +LDFLAGS= ${_LDFLAGS}
  
 -AR= ar rcu