[build] Add macro for testing droid header contents.

m4/check_droid_enum.m4

@@ -0,0 +1,17 @@
+AC_DEFUN([CC_CHECK_DROID_ENUM],
+[AC_MSG_CHECKING([if droid headers have enum $2])
+ AC_LANG_SAVE
+ AC_LANG_C
+ SAVE_CFLAGS="$CFLAGS"
+ CFLAGS="$CFLAGS $1"
+ AC_TRY_COMPILE(
+ [ #include <system/audio.h> ],
+ [ unsigned int e = $2; ],
+ cc_check_droid_enum=yes, cc_check_droid_enum=no)
+ CFLAGS="$SAVE_CFLAGS"
+ AC_LANG_RESTORE
+ AC_MSG_RESULT([$cc_check_droid_enum])
+if test x"$cc_check_droid_enum" = x"yes"; then
+  AC_DEFINE(HAVE_ENUM_$2,,[define if enum $2 is found in headers])
+fi
+])