Fuzzing: Expose DONT_FAIL_ON_CRC_ERROR as a CMake option and honor it in the rar5 decoder (libarchive#2229)

Hey,

the fuzzing infrastructure over at OSSFuzz builds libarchive with the
CMake option `-DDONT_FAIL_ON_CRC_ERROR=1`.

https://github.com/google/oss-fuzz/blob/e4643b64b3af4932bff23bb87afdfbac2a301969/projects/libarchive/build.sh#L35
This, unfortunatly, does not do anything since it's never been defined
as an option.

Building the fuzzers with CRC checks disabled should improve fuzzing
efficacy a bunch.

Thanks!

Author: Mrmaxmeier

CMakeLists.txt

@@ -2173,6 +2173,11 @@ IF(APPLE)
   ADD_DEFINITIONS(-Wno-deprecated-declarations)
 ENDIF(APPLE)
 
+OPTION(DONT_FAIL_ON_CRC_ERROR "Ignore CRC errors during parsing (For fuzzing)" OFF)
+IF(DONT_FAIL_ON_CRC_ERROR)
+  ADD_DEFINITIONS(-DDONT_FAIL_ON_CRC_ERROR=1)
+ENDIF(DONT_FAIL_ON_CRC_ERROR)
+
 IF(ENABLE_TEST)
   ADD_CUSTOM_TARGET(run_all_tests)
 ENDIF(ENABLE_TEST)

libarchive/archive_read_support_format_rar5.c

@@ -2229,10 +2229,12 @@ static int process_base_block(struct archive_read* a,
 	/* Verify the CRC32 of the header data. */
 	computed_crc = (uint32_t) crc32(0, p, (int) hdr_size);
 	if(computed_crc != hdr_crc) {
+#ifndef DONT_FAIL_ON_CRC_ERROR
 		archive_set_error(&a->archive, ARCHIVE_ERRNO_FILE_FORMAT,
 		    "Header CRC error");
 
 		return ARCHIVE_FATAL;
+#endif
 	}
 
 	/* If the checksum is OK, we proceed with parsing. */