Fix `-Wstrict-prototypes`.

* builds/unix/configure.raw: Fix `-Wstrict-prototypes`.
Clang 16 warns on these and they will be dropped in C23.

* builds/unix/freetype2.m4: Ditto.

Signed-off-by: Sam James <sam@gentoo.org>

builds/unix/configure.raw

@@ -50,7 +50,7 @@ if test ${cross_compiling} = yes; then
 
   AC_MSG_CHECKING([for suffix of native executables])
   rm -f a.* b.* a_out.exe conftest.*
-  echo > conftest.c "int main() { return 0;}"
+  echo > conftest.c "int main(void) { return 0;}"
   ${CC_BUILD} conftest.c || AC_MSG_ERROR([native C compiler is not working])
   rm -f conftest.c
   if test -x a.out -o -x b.out -o -x conftest; then

builds/unix/freetype2.m4

@@ -121,7 +121,7 @@ AC_DEFUN([AC_CHECK_FT2],
 #include <stdlib.h>
 
 int
-main()
+main(void)
 {
   FT_Library library;
   FT_Error  error;