Start porting the GL dispatch code to win32.

It now builds successfully builds a .dll file.  Not that it's usable
or anything yet.

configure.ac

@@ -44,6 +44,7 @@ AC_CHECK_PROGS([PYTHON], [python3 python2 python])
 
 # Initialize libtool
 AC_DISABLE_STATIC
+AC_LIBTOOL_WIN32_DLL
 AC_PROG_LIBTOOL
 AC_SYS_LARGEFILE
 
@@ -51,13 +52,22 @@ case $host_os in
     mingw*)
         build_egl=no
         build_glx=no
+        # On windows, the DLL has to have all of its functions
+        # resolved at link time, so we have to link directly aginst
+        # opengl32.dll.  But that's the only GL provider, anyway.
+        EPOXY_LINK_LIBS="-lopengl32"
         ;;
     *)
         build_egl=yes
         build_glx=yes
+        # On platforms with dlopen, we load everything dynamically and
+        # don't link against a specific window system or GL implementation.
+        EPOXY_LINK_LIBS=""
         ;;
 esac
 
+AC_SUBST(EPOXY_LINK_LIBS)
+
 AM_CONDITIONAL(BUILD_EGL, test x$build_egl = xyes)
 if test x$build_egl = xyes; then
     AC_DEFINE([BUILD_EGL], [1], [build EGL tests])
@@ -68,6 +78,13 @@ if test x$build_glx = xyes; then
     AC_DEFINE([BUILD_GLX], [1], [build GLX tests])
 fi
 
+
+case $host_os in
+    mingw*)
+        # visibility flags aren't supported for windows DLLs, and the
+        # compiler whines to tell you so, so don't set them up.
+        ;;
+    *)
         if test "x$GCC" = xyes; then
             save_CFLAGS="$CFLAGS"
             AC_MSG_CHECKING([whether $CC supports -fvisibility=hidden])
@@ -79,6 +96,8 @@ if test "x$GCC" = xyes; then
             # Restore CFLAGS; VISIBILITY_CFLAGS are added to it where needed.
             CFLAGS=$save_CFLAGS
         fi
+        ;;
+esac
 
 AC_SUBST([VISIBILITY_CFLAGS])
 

src/Makefile.am

@@ -93,6 +93,11 @@ libepoxy_la_SOURCES = \
 	$(BUILD_GLX_CODE) \
 	$()
 
+libepoxy_la_LDFLAGS = \
+	-no-undefined \
+        $(EPOXY_LINK_LIBS) \
+	$()
+
 if BUILD_EGL
 BUILD_EGL_CODE = \
 	$(GENERATED_EGL) \

src/dispatch_common.c

@@ -89,27 +89,26 @@
 
 #include <assert.h>
 #include <stdlib.h>
+#ifdef _WIN32
+#include <windows.h>
+#else
 #include <dlfcn.h>
+#include <err.h>
+#include <pthread.h>
+#endif
 #include <string.h>
 #include <ctype.h>
 #include <stdio.h>
-#include <pthread.h>
-#include <err.h>
 
-#include "epoxy/gl.h"
-#if PLATFORM_HAS_GLX
-#include "epoxy/glx.h"
-#endif
-#if PLATFORM_HAS_EGL
-#include "epoxy/egl.h"
-#endif
 #include "dispatch_common.h"
 
 struct api {
+#ifndef _WIN32
     /**
      * Locking for making sure we don't double-dlopen().
      */
     pthread_mutex_t mutex;
+#endif
 
     /** dlopen() return value for libGL.so.1. */
     void *glx_handle;
@@ -139,9 +138,12 @@ struct api {
 };
 
 static struct api api = {
+#ifndef _WIN32
     .mutex = PTHREAD_MUTEX_INITIALIZER,
+#endif
 };
 
+#ifndef _WIN32
 static void
 get_dlopen_handle(void **handle, const char *lib_name, bool exit_on_fail)
 {
@@ -173,6 +175,14 @@ do_dlsym(void **handle, const char *lib_name, const char *name,
 
     return result;
 }
+#else
+static void *
+do_dlsym(void **handle, const char *lib_name, const char *name,
+         bool exit_on_fail)
+{
+    return NULL;
+}
+#endif
 
 PUBLIC bool
 epoxy_is_desktop_gl(void)
@@ -331,6 +341,9 @@ epoxy_gles2_dlsym(const char *name)
 void *
 epoxy_get_proc_address(const char *name)
 {
+#ifdef _WIN32
+    return wglGetProcAddress(name);
+#else
     if (api.egl_handle) {
         return eglGetProcAddress(name);
     } else if (api.glx_handle) {
@@ -370,6 +383,7 @@ epoxy_get_proc_address(const char *name)
 
         errx(1, "Couldn't find GLX or EGL libraries.\n");
     }
+#endif
 }
 
 void
@@ -395,9 +409,13 @@ epoxy_print_failure_reasons(const char *name,
 PUBLIC void
 epoxy_glBegin(GLenum primtype)
 {
+#ifdef _WIN32
+#warning missing locking
+#else
     pthread_mutex_lock(&api.mutex);
     api.begin_count++;
     pthread_mutex_unlock(&api.mutex);
+#endif
 
     epoxy_glBegin_unwrapped(primtype);
 }
@@ -407,7 +425,11 @@ epoxy_glEnd(void)
 {
     epoxy_glEnd_unwrapped();
 
+#ifdef _WIN32
+#warning missing locking
+#else
     pthread_mutex_lock(&api.mutex);
     api.begin_count--;
     pthread_mutex_unlock(&api.mutex);
+#endif
 }

src/dispatch_common.h

@@ -40,7 +40,9 @@
 #endif
 
 #ifndef PUBLIC
-#  if (defined(__GNUC__) && __GNUC__ >= 4) || (defined(__SUNPRO_C) && (__SUNPRO_C >= 0x590))
+#  ifdef _WIN32
+#    define PUBLIC __declspec(dllexport)
+#  elif (defined(__GNUC__) && __GNUC__ >= 4) || (defined(__SUNPRO_C) && (__SUNPRO_C >= 0x590))
 #    define PUBLIC __attribute__((visibility("default")))
 #  else
 #    define PUBLIC