Export a few glapi functions used by gallium and r300

Fixes breakage from -fvisibility-hidden commit.

src/mesa/glapi/glapi.c

@@ -237,7 +237,7 @@ PUBLIC void *_glapi_Context = NULL;
  * We should call this periodically from a function such as glXMakeCurrent
  * in order to test if multiple threads are being used.
  */
-void
+PUBLIC void
 _glapi_check_multithread(void)
 {
 #if defined(THREADS) && !defined(GLX_USE_TLS)

src/mesa/glapi/glapi_getproc.c

@@ -530,7 +530,7 @@ _glapi_get_proc_offset(const char *funcName)
  * in the name of static functions, try generating a new API entrypoint on
  * the fly with assembly language.
  */
-_glapi_proc
+PUBLIC _glapi_proc
 _glapi_get_proc_address(const char *funcName)
 {
    struct _glapi_function * entry;

src/mesa/glapi/glthread.c

@@ -69,7 +69,7 @@
  */
 #ifdef PTHREADS
 
-unsigned long
+PUBLIC unsigned long
 _glthread_GetID(void)
 {
    return (unsigned long) pthread_self();
@@ -123,7 +123,7 @@ _glthread_SetTSD(_glthread_TSD *tsd, void *ptr)
 #define USE_LOCK_FOR_KEY	/* undef this to try a version without
 				   lock for the global key... */
 
-unsigned long
+PUBLIC unsigned long
 _glthread_GetID(void)
 {
    abort();   /* XXX not implemented yet */
@@ -201,7 +201,7 @@ void InsteadOf_exit(int nCode)
    DWORD dwErr=GetLastError();
 }
 
-unsigned long
+PUBLIC unsigned long
 _glthread_GetID(void)
 {
    return GetCurrentThreadId();
@@ -251,7 +251,7 @@ _glthread_SetTSD(_glthread_TSD *tsd, void *ptr)
  */
 #ifdef BEOS_THREADS
 
-unsigned long
+PUBLIC unsigned long
 _glthread_GetID(void)
 {
    return (unsigned long) find_thread(NULL);
@@ -293,7 +293,7 @@ _glthread_SetTSD(_glthread_TSD *tsd, void *ptr)
  * no-op functions
  */
 
-unsigned long
+PUBLIC unsigned long
 _glthread_GetID(void)
 {
    return 0;