bugfix 'echo -n' is not POSIX, use input redirection from /dev/null

Makefile

@@ -158,7 +158,7 @@ ifndef AFL_NO_X86
 test_build: afl-gcc afl-as afl-showmap
 	@echo "[*] Testing the CC wrapper and instrumentation output..."
 	unset AFL_USE_ASAN AFL_USE_MSAN AFL_CC; AFL_QUIET=1 AFL_INST_RATIO=100 AFL_PATH=. ./$(TEST_CC) $(CFLAGS) test-instr.c -o test-instr $(LDFLAGS)
-	echo -n| ./afl-showmap -m none -q -o .test-instr0 ./test-instr
+	./afl-showmap -m none -q -o .test-instr0 ./test-instr </dev/null
 	echo 1 | ./afl-showmap -m none -q -o .test-instr1 ./test-instr
 	@rm -f test-instr
 	@cmp -s .test-instr0 .test-instr1; DR="$$?"; rm -f .test-instr0 .test-instr1; if [ "$$DR" = "0" ]; then echo; echo "Oops, the instrumentation does not seem to be behaving correctly!"; echo; echo "Please ping <lcamtuf@google.com> to troubleshoot the issue."; echo; exit 1; fi

llvm_mode/Makefile

@@ -174,7 +174,7 @@ endif
 test_build: $(PROGS)
 	@echo "[*] Testing the CC wrapper and instrumentation output..."
 	unset AFL_USE_ASAN AFL_USE_MSAN AFL_INST_RATIO; AFL_QUIET=1 AFL_PATH=. AFL_CC=$(CC) AFL_LLVM_LAF_SPLIT_SWITCHES=1 AFL_LLVM_LAF_TRANSFORM_COMPARES=1 AFL_LLVM_LAF_SPLIT_COMPARES=1 ../afl-clang-fast $(CFLAGS) ../test-instr.c -o test-instr $(LDFLAGS)
-	echo -n| ../afl-showmap -m none -q -o .test-instr0 ./test-instr
+	../afl-showmap -m none -q -o .test-instr0 ./test-instr </dev/null
 	echo 1 | ../afl-showmap -m none -q -o .test-instr1 ./test-instr
 	@rm -f test-instr
 	@cmp -s .test-instr0 .test-instr1; DR="$$?"; rm -f .test-instr0 .test-instr1; if [ "$$DR" = "0" ]; then echo; echo "Oops, the instrumentation does not seem to be behaving correctly!"; echo; echo "Please ping <lcamtuf@google.com> to troubleshoot the issue."; echo; exit 1; fi