tools: exclude benchmark code from coverage report

Refs: nodejs/build#1676 (comment)

PR-URL: #25841
Reviewed-By: Richard Lau <riclau@uk.ibm.com>
Reviewed-By: Ben Coe <bencoe@gmail.com>
Reviewed-By: Colin Ihrig <cjihrig@gmail.com>
Reviewed-By: Michael Dawson <michael_dawson@ca.ibm.com>
Reviewed-By: Refael Ackermann <refack@gmail.com>
Reviewed-By: Anna Henningsen <anna@addaleax.net>

Makefile

@@ -242,7 +242,7 @@ coverage-test: coverage-build
 
 COV_REPORT_OPTIONS = --reporter=html \
 	--temp-directory=out/$(BUILDTYPE)/.coverage --omit-relative=false \
-	--resolve=./lib --exclude="deps/" --exclude="test/" --exclude="tools/" \
+	--resolve=./lib --exclude="benchmark/" --exclude="deps/" --exclude="test/" --exclude="tools/" \
 	--wrapper-length=0
 ifdef COV_ENFORCE_THRESHOLD
   COV_REPORT_OPTIONS += --check-coverage --lines=$(COV_ENFORCE_THRESHOLD)