Rework symbol visibility for easier maintenance

Save in a few special cases, _X_EXPORT should not be used in C source
files. Instead, it should be used in headers, and the proper C source
include that header. Some special cases are symbols that need to be
shared between modules, but not expected to be used by external drivers,
and symbols that are accessible via LoaderSymbol/dlopen.

  This patch also adds conditionally some new sdk header files, depending
on extensions enabled. These files were added to match pattern for
other extensions/modules, that is, have the headers "deciding" symbol
visibility in the sdk. These headers are:
o Xext/panoramiXsrv.h, Xext/panoramiX.h
o fbpict.h (unconditionally)
o vidmodeproc.h
o mioverlay.h (unconditionally, used only by xaa)
o xfixes.h (unconditionally, symbols required by dri2)

  LoaderSymbol and similar functions now don't have different prototypes,
in loaderProcs.h and xf86Module.h, so that both headers can be included,
without the need of defining IN_LOADER.

  xf86NewInputDevice() device prototype readded to xf86Xinput.h, but
not exported (and with a comment about it).

render/glyphstr.h

@@ -91,58 +91,58 @@ typedef struct _GlyphList {
     PictFormatPtr   format;
 } GlyphListRec, *GlyphListPtr;
 
-GlyphHashSetPtr
+extern _X_EXPORT GlyphHashSetPtr
 FindGlyphHashSet (CARD32 filled);
 
-void
+extern _X_EXPORT void
 GlyphUninit (ScreenPtr pScreen);
 
-GlyphHashSetPtr
+extern _X_EXPORT GlyphHashSetPtr
 FindGlyphHashSet (CARD32 filled);
 
-GlyphRefPtr
+extern _X_EXPORT GlyphRefPtr
 FindGlyphRef (GlyphHashPtr	hash,
 	      CARD32		signature,
 	      Bool		match,
 	      unsigned char	sha1[20]);
 
-GlyphPtr
+extern _X_EXPORT GlyphPtr
 FindGlyphByHash (unsigned char sha1[20], int format);
 
-int
+extern _X_EXPORT int
 HashGlyph (xGlyphInfo    *gi,
 	   CARD8	 *bits,
 	   unsigned long size,
 	   unsigned char sha1[20]);
 
-void
+extern _X_EXPORT void
 FreeGlyph (GlyphPtr glyph, int format);
 
-void
+extern _X_EXPORT void
 AddGlyph (GlyphSetPtr glyphSet, GlyphPtr glyph, Glyph id);
 
-Bool
+extern _X_EXPORT Bool
 DeleteGlyph (GlyphSetPtr glyphSet, Glyph id);
 
-GlyphPtr
+extern _X_EXPORT GlyphPtr
 FindGlyph (GlyphSetPtr glyphSet, Glyph id);
 
-GlyphPtr
+extern _X_EXPORT GlyphPtr
 AllocateGlyph (xGlyphInfo *gi, int format);
 
-Bool
+extern _X_EXPORT Bool
 AllocateGlyphHash (GlyphHashPtr hash, GlyphHashSetPtr hashSet);
 
-Bool
+extern _X_EXPORT Bool
 ResizeGlyphHash (GlyphHashPtr hash, CARD32 change, Bool global);
 
-Bool
+extern _X_EXPORT Bool
 ResizeGlyphSet (GlyphSetPtr glyphSet, CARD32 change);
 
-GlyphSetPtr
+extern _X_EXPORT GlyphSetPtr
 AllocateGlyphSet (int fdepth, PictFormatPtr format);
 
-int
+extern _X_EXPORT int
 FreeGlyphSet (pointer   value,
 	      XID       gid);