Change awk script to be able to work on MacOS as well (#1136)

kokoro/presubmit/presubmit.sh

@@ -88,7 +88,7 @@ function run_enumerate_tests() {
   TARGETS="$($BAZEL query --deleted_packages=//gapii/fuchsia --output label 'kind(".*_test rule", //...)' | sort -t: -k1,1 | awk '{print "        \""$0"\","}')"
   OUT=$(mktemp)
   cp BUILD.bazel $OUT
-  cat $OUT | awk -v targets="$TARGETS" 'begin {a=0} /__END_TESTS/ {a=0} { if (a==0) print $0;} /__BEGIN_TESTS/ { a=1; print targets }' > BUILD.bazel
+  cat $OUT | awk -v "targets=${TARGETS//$'\n'/\\n}" 'begin {a=0} /__END_TESTS/ {a=0} { if (a==0) print $0;} /__BEGIN_TESTS/ { a=1; print targets }' > BUILD.bazel
 }
 
 function run_gazelle() {