Support for using honggfuzz with gcc

[simonresch]

Adds the flag --@rules_fuzzing//fuzzing:compiler_type with possible configurations cmake and gcc. This allows running honggfuzz with a gcc toolchain which can be useful for code bases that don't compile with clang or where no clang toolchain is available.

Example usage:

bazel run //examples:re2_fuzz_test --config asan-honggfuzz-gcc

Invalid engine / compiler combination:

$ bazel run //examples:re2_fuzz_test --config asan-libfuzzer --@rules_fuzzing//fuzzing:compiler_type=gcc
WARNING: Build options --//fuzzing:cc_engine and --//fuzzing:cc_engine_instrumentation have changed, discarding analysis cache (this can be expensive, see https://bazel.build/advanced/performance/iteration-speed).
ERROR: Traceback (most recent call last):
	File "/home/simon/git/rules_fuzzing/fuzzing/private/binary.bzl", line 67, column 13, in _fuzzing_binary_transition_impl
		fail("unsupported engine instrumentation '%s' for compiler '%s'" % (instrum_config, compiler_type))
Error in fail: unsupported engine instrumentation 'libfuzzer' for compiler 'gcc'

[simonresch]

Ping @stefanbucur. Is there any interest in adding this?

[fmeum]

This could be replaced with the predefined settings in @rules_cc//cc/compiler. Then we don't need compiler_type at all as the choice will be determined by the C++ toolchain.

[simonresch]

I originally attempted something based on @rules_cc//cc/compiler but got stuck on this error

ERROR: .../rules_fuzzing/examples/java/BUILD:31:15: On dependency edge //examples/java:EmptyFuzzTest_bin (3b35bd8) -|binary|-> //examples/java:EmptyFuzzTest_raw_: attempting to transition on '@@rules_cc+//cc/compiler:gcc' which is not a build setting

when adding @rules_cc//cc/compiler:gcc as an input to the fuzzing_binary_transition transition. Do you have an idea how to access the compiler type from the transition without it being an explicit flag?

[fmeum]

I followed up on bazelbuild/rules_cc#435. If we had that, we could read the compiler from an implicit attribute of the fuzzing_binary rule.

Let's wait for a few days before we look into alternatives.

[fmeum]

It's in now, we would just need to update rules_cc.