Quick question - are you using the "extra" repo? While I have no need to use GLX, I did install glxinfo for shitz n giggles using "extra"
Seemed to work for me - then again and as I mentioned, I have no reason to use it so my test very well could be invalid.
BTW, running glxgears did produce the spinning gears to my surprise.
and running pacman -Qs mesa produced the smae output as yours.
The diffs could be the video card and drivers - I never use Nvidia cards.
name of display: :0
display: :0 screen: 0
direct rendering: Yes
server glx vendor string: SGI
server glx version string: 1.4
server glx extensions:
GLX_ARB_context_flush_control, GLX_ARB_create_context,
GLX_ARB_create_context_no_error, GLX_ARB_create_context_profile,
GLX_ARB_create_context_robustness, GLX_ARB_fbconfig_float,
GLX_ARB_framebuffer_sRGB, GLX_ARB_multisample,
GLX_EXT_create_context_es2_profile, GLX_EXT_create_context_es_profile,
GLX_EXT_fbconfig_packed_float, GLX_EXT_framebuffer_sRGB,
GLX_EXT_get_drawable_type, GLX_EXT_libglvnd, GLX_EXT_no_config_context,
GLX_EXT_texture_from_pixmap, GLX_EXT_visual_info, GLX_EXT_visual_rating,
GLX_INTEL_swap_event, GLX_MESA_copy_sub_buffer, GLX_OML_swap_method,
GLX_SGIS_multisample, GLX_SGIX_fbconfig, GLX_SGIX_pbuffer,
GLX_SGIX_visual_select_group, GLX_SGI_make_current_read,
GLX_SGI_swap_control
client glx vendor string: Mesa Project and SGI
client glx version string: 1.4