cmake: remove USE_SANITIZER and USE_COVERAGE options

Both the USE_SANITIZER and USE_COVERAGE options are convenience options
that turn on a set of CFLAGS. Despite our own set of CFLAGS required to
build libgit2, we have no real business to mess with them, though, as
they can easily be passed in by the user via specifying the CFLAGS
environment variable. The reasoning behind not providing them is that as
soon as we start adding those for some usecases, users might ask for
other sets of CFLAGS catering to their specific need in another usecase.
Thus, we do not want to support them here.

CMakeLists.txt

@@ -54,8 +54,6 @@ OPTION(LIBGIT2_FILENAME			"Name of the produced binary"				OFF)
 OPTION(USE_SSH				"Link with libssh to enable SSH support"		 ON)
 OPTION(USE_HTTPS			"Enable HTTPS support. Can be set to a specific backend" ON)
 OPTION(USE_GSSAPI			"Link with libgssapi for SPNEGO auth"			OFF)
-OPTION(USE_SANITIZER			"Enable one of the Sanitizers (requires clang)"		OFF)
-OPTION(USE_COVERAGE			"Enable clang's coverage report (requires clang)"	OFF)
 OPTION(USE_STANDALONE_FUZZERS		"Enable standalone fuzzers (compatible with gcc)"	OFF)
 OPTION(VALGRIND				"Configure build for valgrind"				OFF)
 OPTION(CURL				"Use curl for HTTP if available"			 ON)
@@ -250,20 +248,6 @@ ELSE()
 	# that uses CMAKE_CONFIGURATION_TYPES and not CMAKE_BUILD_TYPE
 ENDIF()
 
-IF(NOT USE_SANITIZER STREQUAL "OFF")
-	# Workaround to force linking against -lasan
-	SET(CMAKE_REQUIRED_FLAGS "-fsanitize=${USE_SANITIZER}")
-	ADD_C_FLAG(-fsanitize=${USE_SANITIZER})
-	UNSET(CMAKE_REQUIRED_FLAGS)
-	ADD_C_FLAG(-fno-omit-frame-pointer)
-	ADD_C_FLAG(-fno-optimize-sibling-calls)
-ENDIF()
-
-IF(USE_COVERAGE)
-	ADD_C_FLAG(-fcoverage-mapping)
-	ADD_C_FLAG(-fprofile-instr-generate)
-ENDIF()
-
 IF(BUILD_FUZZERS AND NOT USE_STANDALONE_FUZZERS)
 	# The actual sanitizer link target will be added when linking the fuzz
 	# targets.

docs/fuzzing.md

@@ -18,10 +18,10 @@ automated fuzz testing. libFuzzer only works with clang.
    [`undefined`](https://clang.llvm.org/docs/UndefinedBehaviorSanitizer.html),
    and [`leak`/`address,leak`](https://clang.llvm.org/docs/LeakSanitizer.html).
 3. Create the cmake build environment and configure the build with the
-   sanitizer chosen: `CC=/usr/bin/clang-6.0 cmake
-   -DBUILD_CLAR=OFF -DBUILD_FUZZERS=ON -DUSE_SANITIZER=address
-   -DCMAKE_BUILD_TYPE=RelWithDebInfo ..`. Note that building the fuzzer targets
-   is incompatible with the tests and examples.
+   sanitizer chosen: `CC=/usr/bin/clang-6.0 CFLAGS="-fsanitize=address" cmake
+   -DBUILD_CLAR=OFF -DBUILD_FUZZERS=ON -DCMAKE_BUILD_TYPE=RelWithDebInfo ..`.
+   Note that building the fuzzer targets is incompatible with the
+   tests and examples.
 4. Build libgit2: `cmake --build .`
 5. Exit the cmake build environment: `cd ..`
 
@@ -38,8 +38,8 @@ will write the coverage report.
 
 ## Get coverage
 
-In order to get coverage information, you also need to add the
-`-DUSE_COVERAGE=ON` flag to `cmake`, and then run the fuzz target with
+In order to get coverage information, you need to add the "-fcoverage-mapping"
+and "-fprofile-instr-generate CFLAGS, and then run the fuzz target with
 `-runs=0`. That will produce a file called `default.profraw` (this behavior can
 be overridden by setting the `LLVM_PROFILE_FILE="yourfile.profraw"` environment
 variable).