nir/algebraic: Fail build when too many commutative expressions are used

Search patterns that are expected to have too many (e.g., the giant
bitfield_reverse pattern) can be added to a white list.

This would have saved me a few hours debugging. :(

v2: Implement the expected-failure annotation as a property of the
search-replace pattern instead of as a property of the whole list of
patterns.  Suggested by Connor.

Reviewed-by: Connor Abbott <cwabbott0@gmail.com>
Reviewed-by: Dylan Baker <dylan@pnwbakers.com>

src/compiler/nir/nir_search.c

@@ -30,6 +30,7 @@
 #include "nir_builder.h"
 #include "util/half_float.h"
 
+/* This should be the same as nir_search_max_comm_ops in nir_algebraic.py. */
 #define NIR_SEARCH_MAX_COMM_OPS 4
 
 struct match_state {