Decorate qsort callbacks with cdecl.

* include/freetype/internal/compiler-macros.h (FT_COMPARE_DEF):
Add new macro.
* src/base/ftrfork.c, src/bdf/bdflib.c, src/gxvalid/gxvcommn.c,
src/psaux/afmparse.c, src/psnames/psmodule.c, src/type1/t1afm.c,
src/sfnt/sfwoff.c, src/sfnt/sfwoff2.c: Update qsort callbacks.

Fixes #1026 when compiling FreeType with an unusual calling convention
while the C library qsort still expects cdecl.
diff --git a/src/bdf/bdflib.c b/src/bdf/bdflib.c
index b494a09..e62f09a 100644
--- a/src/bdf/bdflib.c
+++ b/src/bdf/bdflib.c
@@ -807,7 +807,7 @@
 
 
   /* Routine to compare two glyphs by encoding so they can be sorted. */
-  static int
+  FT_COMPARE_DEF( int )
   by_encoding( const void*  a,
                const void*  b )
   {