Issue #25188: Add a -P/--pgo flag to regrtest to silence error output.

Since PGO building doesn't care about test failures, silence them when
running the test suite for performance reasons. Initial patch by
Alecsandru Patrascu of Intel.

Makefile.pre.in

@@ -231,7 +231,7 @@ TCLTK_INCLUDES=	@TCLTK_INCLUDES@
 TCLTK_LIBS=	@TCLTK_LIBS@
 
 # The task to run while instrument when building the profile-opt target
-PROFILE_TASK=-m test.regrtest >/dev/null 2>&1
+PROFILE_TASK=-m test.regrtest --pgo
 
 # report files for gcov / lcov coverage report
 COVERAGE_INFO=	$(abs_builddir)/coverage.info