gallium/compute: Add PIPE_COMPUTE_CAP_IR_TARGET v4

v2: Tom Stellard
  - Update CAP description

v3: Tom Stellard
  - TGSI targets should pass an empty string for this CAP.

v4: Tom Stellard
  - TGSI targets can ignore this CAP.

Reviewed-by: Francisco Jerez <currojerez@riseup.net>

src/gallium/docs/source/screen.rst

@@ -212,6 +212,11 @@ PIPE_COMPUTE_CAP_*
 Compute-specific capabilities. They can be queried using
 pipe_screen::get_compute_param.
 
+* ``PIPE_COMPUTE_CAP_IR_TARGET``: A description of the target as a target
+  triple specification of the form ``processor-manufacturer-os`` that will
+  be passed on to the compiler.  This CAP is only relevant for drivers
+  that specify PIPE_SHADER_IR_LLVM for their preferred IR.
+  Value type: null-terminated string.
 * ``PIPE_COMPUTE_CAP_GRID_DIMENSION``: Number of supported dimensions
   for grid and block coordinates.  Value type: ``uint64_t``.
 * ``PIPE_COMPUTE_CAP_MAX_GRID_SIZE``: Maximum grid size in block

src/gallium/include/pipe/p_defines.h

@@ -546,6 +546,7 @@ enum pipe_shader_ir
  */
 enum pipe_compute_cap
 {
+   PIPE_COMPUTE_CAP_IR_TARGET,
    PIPE_COMPUTE_CAP_GRID_DIMENSION,
    PIPE_COMPUTE_CAP_MAX_GRID_SIZE,
    PIPE_COMPUTE_CAP_MAX_BLOCK_SIZE,