gallivm: add mask api to force mask

For per-sample shading the mask needs to be forced for each
iteration of the fragment shader.

Just adds the API for now.

Reviewed-by: Roland Scheidegger <sroland@vmware.com>
Part-of: <https://gitlab.freedesktop.org/mesa/mesa/-/merge_requests/4122>

src/gallium/auxiliary/gallivm/lp_bld_flow.c

@@ -200,6 +200,16 @@ lp_build_mask_update(struct lp_build_mask_context *mask,
    LLVMBuildStore(mask->skip.gallivm->builder, value, mask->var);
 }
 
+/*
+ * Update boolean mask with given value.
+ * Used for per-sample shading to force per-sample execution masks.
+ */
+void
+lp_build_mask_force(struct lp_build_mask_context *mask,
+                    LLVMValueRef value)
+{
+   LLVMBuildStore(mask->skip.gallivm->builder, value, mask->var);
+}
 
 /**
  * End section of code which is predicated on a mask.

src/gallium/auxiliary/gallivm/lp_bld_flow.h

@@ -94,6 +94,10 @@ void
 lp_build_mask_update(struct lp_build_mask_context *mask,
                      LLVMValueRef value);
 
+void
+lp_build_mask_force(struct lp_build_mask_context *mask,
+                    LLVMValueRef value);
+
 void
 lp_build_mask_check(struct lp_build_mask_context *mask);