intel/compiler/test: use TEST_DEBUG env var consistently

Other tests use the same environment variable to decide whether they
should print debugging information.

Will quiet Coverity's "'Constant' variable guards dead code".

Signed-off-by: Marcin Ślusarz <marcin.slusarz@intel.com>
Reviewed-by: Lionel Landwerlin <lionel.g.landwerlin@intel.com>
Part-of: <https://gitlab.freedesktop.org/mesa/mesa/-/merge_requests/6126>

src/intel/compiler/test_vec4_copy_propagation.cpp

@@ -105,7 +105,7 @@ void copy_propagation_test::SetUp()
 static void
 copy_propagation(vec4_visitor *v)
 {
-   bool print = false;
+   const bool print = getenv("TEST_DEBUG");
 
    if (print) {
       fprintf(stderr, "instructions before:\n");

src/intel/compiler/test_vec4_dead_code_eliminate.cpp

@@ -103,7 +103,7 @@ void dead_code_eliminate_test::SetUp()
 static void
 dead_code_eliminate(vec4_visitor *v)
 {
-   bool print = false;
+   const bool print = getenv("TEST_DEBUG");
 
    if (print) {
       fprintf(stderr, "instructions before:\n");

src/intel/compiler/test_vec4_register_coalesce.cpp

@@ -108,7 +108,7 @@ void register_coalesce_test::SetUp()
 static void
 _register_coalesce(vec4_visitor *v, const char *func)
 {
-   bool print = false;
+   const bool print = getenv("TEST_DEBUG");
 
    if (print) {
       printf("%s: instructions before:\n", func);