Significantly reduce compile time for googletest internal tests

Clang's optimizer spends a really long time on these tests at -O2, so we now
use -O0 instead. This reduces the -j32 time for lib/googletest/test from 131s
to 29s. Using -O0 also reduces the disk usage from 144MB (at -O2) / 92MB (at
-O1) to 82MB.

Reviewed By:	ngie, dim
Differential Revision: https://reviews.freebsd.org/D26751

lib/googletest/tests/Makefile.inc

@@ -4,3 +4,15 @@
 # Keep the existing tests directory structure (with subdirs per component)
 # rather than installing all of them to /usr/tests/lib/googletest
 TESTSDIR=	${TESTSBASE}/lib/googletest/${.CURDIR:T}
+
+# Clang's optimizer spends a really long time on these tests at -O2. Changing
+# -O2 to -O1 reduces the -j32 time for lib/googletest/test from 131s to 71s.
+# Using -O0 further reduces the time to 29s, and also reduces the disk usage
+# from 144MB (at -O2) / 92MB (at -O1) to 82MB, so we use -O0.
+# Note: Building without debug info saves about 10-15% of the build time, so we
+# only enable debug info if DEBUG_FLAGS is not empty (71s -> 64s at -O1 and -j32).
+CFLAGS.clang+=	-O0
+.if empty(DEBUG_FLAGS)
+MK_DEBUG_FILES:=no
+CFLAGS.clang+=	-g0
+.endif