[PATCH v2] Makefile: use FUZZ_CXXFLAGS for linking fuzzers

[Josh Steadmon <steadmon@google.com>]

OSS-Fuzz requires C++-specific flags to link fuzzers. Passing these in
CFLAGS causes lots of build warnings. Using separate FUZZ_CXXFLAGS
avoids this.

Signed-off-by: Josh Steadmon <steadmon@google.com>
---
Since there's nothing else using CXXFLAGS, let's just make it explicit
that these apply to the fuzzers.


Range-diff against v1:
1:  1630a93f82 < -:  ---------- Makefile: use CXXFLAGS for linking fuzzers
-:  ---------- > 1:  6b3d6dd7f0 Makefile: use FUZZ_CXXFLAGS for linking fuzzers

 Makefile | 6 ++++--
 1 file changed, 4 insertions(+), 2 deletions(-)

diff --git a/Makefile b/Makefile
index bbfbb4292d..0c05896797 100644
--- a/Makefile
+++ b/Makefile
@@ -3098,14 +3098,16 @@ cover_db_html: cover_db
 # An example command to build against libFuzzer from LLVM 4.0.0:
 #
 # make CC=clang CXX=clang++ \
-#      CFLAGS="-fsanitize-coverage=trace-pc-guard -fsanitize=address" \
+#      FUZZ_CXXFLAGS="-fsanitize-coverage=trace-pc-guard -fsanitize=address" \
 #      LIB_FUZZING_ENGINE=/usr/lib/llvm-4.0/lib/libFuzzer.a \
 #      fuzz-all
 #
+FUZZ_CXXFLAGS ?= $(CFLAGS)
+
 .PHONY: fuzz-all
 
 $(FUZZ_PROGRAMS): all
-	$(QUIET_LINK)$(CXX) $(CFLAGS) $(LIB_OBJS) $(BUILTIN_OBJS) \
+	$(QUIET_LINK)$(CXX) $(FUZZ_CXXFLAGS) $(LIB_OBJS) $(BUILTIN_OBJS) \
 		$(XDIFF_OBJS) $(EXTLIBS) git.o $@.o $(LIB_FUZZING_ENGINE) -o $@
 
 fuzz-all: $(FUZZ_PROGRAMS)
-- 
2.19.1.930.g4563a0d9d0-goog