[ossfuzz] Fix parallel builds

With `make -j` multiple builds of `standaloneengine.o` happened in
parallel. Fix this by detecting `standaloneengine.o` and moving it to a
depedency.

diff --git a/ossfuzz/Makefile b/ossfuzz/Makefile
index f247405395c14df0d123ed95ddb0637a1c14499d..2ec167559a3f09ab894a466c039c0bbd9a33af67 100644 (file)
--- a/ossfuzz/Makefile
+++ b/ossfuzz/Makefile
@@ -26,7 +26,7 @@
 # ##########################################################################
 
 LZ4DIR  := ../lib
-LIB_FUZZING_ENGINE ?= standaloneengine.o
+LIB_FUZZING_ENGINE ?=
 
 DEBUGLEVEL?= 1
 DEBUGFLAGS = -g -DLZ4_DEBUG=$(DEBUGLEVEL)
@@ -59,12 +59,12 @@ $(LZ4DIR)/liblz4.a:
        $(CC) -c $(LZ4_CFLAGS) $(LZ4_CPPFLAGS) $< -o $@
 
 # Generic rule for generating fuzzers
-%_fuzzer: %_fuzzer.o lz4_helpers.o fuzz_data_producer.o $(LZ4DIR)/liblz4.a
-       # Compile the standalone code just in case. The OSS-Fuzz code might
-       # override the LIB_FUZZING_ENGINE value to "-fsanitize=fuzzer"
-       $(CC) -c $(LZ4_CFLAGS) $(LZ4_CPPFLAGS) standaloneengine.c -o standaloneengine.o
-
-       # Now compile the actual fuzzer.
+ifeq ($(LIB_FUZZING_ENGINE),)
+  LIB_FUZZING_DEPS := standaloneengine.o
+else
+  LIB_FUZZING_DEPS :=
+endif
+%_fuzzer: %_fuzzer.o lz4_helpers.o fuzz_data_producer.o $(LZ4DIR)/liblz4.a $(LIB_FUZZING_DEPS)
        $(CXX) $(LZ4_CXXFLAGS) $(LZ4_CPPFLAGS) $(LDFLAGS) $(LIB_FUZZING_ENGINE) $^ -o $@$(EXT)
 
 %_fuzzer_clean: