decouple internal.h headers

Saves comitters' daily life by avoid #include-ing everything from
internal.h to make each file do so instead.  This would significantly
speed up incremental builds.

We take the following inclusion order in this changeset:

1.  "ruby/config.h", where _GNU_SOURCE is defined (must be the very
    first thing among everything).
2.  RUBY_EXTCONF_H if any.
3.  Standard C headers, sorted alphabetically.
4.  Other system headers, maybe guarded by #ifdef
5.  Everything else, sorted alphabetically.

Exceptions are those win32-related headers, which tend not be self-
containing (headers have inclusion order dependencies).

1 files changed, 11 insertions, 2 deletions

diff --git a/math.c b/math.c
index d98467ca0a..7edde60270 100644
--- a/math.c
+++ b/math.c
@@ -9,13 +9,22 @@
 
 **********************************************************************/
 
+#include "ruby/config.h"
+
 #ifdef _MSC_VER
 # define _USE_MATH_DEFINES 1
 #endif
-#include "internal.h"
+
+#include <errno.h>
 #include <float.h>
 #include <math.h>
-#include <errno.h>
+
+#include "internal.h"
+#include "internal/bignum.h"
+#include "internal/complex.h"
+#include "internal/math.h"
+#include "internal/object.h"
+#include "internal/vm.h"
 
 #if defined(HAVE_SIGNBIT) && defined(__GNUC__) && defined(__sun) && \
     !defined(signbit)