mapi: Hide OpenGL functions to be exported when shared-glapi is disabled

Fixes the following test error:
135/154 mesa:gallium / osmesa-symbols-check                                                                       FAIL             0.07s   exit status 1

```
src/gallium/targets/osmesa/libOSMesa.so.8.0.0: unknown symbol exported: glAreTexturesResidentEXT
src/gallium/targets/osmesa/libOSMesa.so.8.0.0: unknown symbol exported: glDeleteTexturesEXT
src/gallium/targets/osmesa/libOSMesa.so.8.0.0: unknown symbol exported: glGenTexturesEXT
src/gallium/targets/osmesa/libOSMesa.so.8.0.0: unknown symbol exported: glIsTextureEXT
```
The build options is:
```
-D glx=xlib -D gles1=disabled -D gles2=disabled -D shared-glapi=disabled
```

Signed-off-by: Yonggang Luo <luoyonggang@gmail.com>
Reviewed-by: Corentin Noël <corentin.noel@collabora.com>
Part-of: <https://gitlab.freedesktop.org/mesa/mesa/-/merge_requests/23409>

meson.build

@@ -779,10 +779,12 @@ if with_clc
 endif
 
 gl_pkgconfig_c_flags = []
+with_glx_indirect_rendering = false
 if with_platform_x11
   if with_glx == 'xlib'
     pre_args += '-DUSE_XSHM'
   else
+    with_glx_indirect_rendering = true
     pre_args += '-DGLX_INDIRECT_RENDERING'
     if with_glx_direct
       pre_args += '-DGLX_DIRECT_RENDERING'
@@ -797,6 +799,13 @@ if with_platform_x11
   endif
 endif
 
+with_glapi_export_proto_entry_points = false
+if with_shared_glapi and not with_glx_indirect_rendering
+  # Imply !defined(GLX_INDIRECT_RENDERING)
+  with_glapi_export_proto_entry_points = true
+endif
+pre_args += '-DGLAPI_EXPORT_PROTO_ENTRY_POINTS=@0@'.format(with_glapi_export_proto_entry_points ? '1' : '0')
+
 with_android_stub = get_option('android-stub')
 if with_android_stub and not with_platform_android
   error('`-D android-stub=true` makes no sense without `-D platforms=android`')