build: fix check for -fsanitize-coverage-allowlist

The existing check has two problems:
1. Meson uses a private directory for the get_supported_arguments check.
./instrumentation-filter does not exist in that private directory (it is
copied into the root of the build-directory).

2. fsanitize-coverage-allowlist is unused when coverage instrumentation
is not configured. No instrumentation are passed for the
get_supported_arguments check

Thus the check always fails. To work around this, change the check to an
"if cc.compiles" check and provide /dev/null, instead of the real
filter.

Meson log:
Working directory:  build/meson-private/tmpl6wld2d9
Command line:  clang-13 -m64 -mcx16
build/meson-private/tmpl6wld2d9/output.obj -c -O3 -D_FILE_OFFSET_BITS=64
-O0 -Werror=implicit-function-declaration -Werror=unknown-warning-option
-Werror=unused-command-line-argument
-Werror=ignored-optimization-argument
-fsanitize-coverage-allowlist=instrumentation-filter

Error:
error: argument unused during compilation:
'-fsanitize-coverage-allowlist=instrumentation-filter'

Signed-off-by: Alexander Bulekov <alxndr@bu.edu>
Message-Id: <20220614155415.4023833-1-alxndr@bu.edu>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>

meson.build

@@ -209,9 +209,13 @@ if get_option('fuzzing')
   configure_file(output: 'instrumentation-filter',
                  input: 'scripts/oss-fuzz/instrumentation-filter-template',
                  copy: true)
-  add_global_arguments(
-      cc.get_supported_arguments('-fsanitize-coverage-allowlist=instrumentation-filter'),
+
+  if cc.compiles('int main () { return 0; }',
+                  name: '-fsanitize-coverage-allowlist=/dev/null',
+                 args: ['-fsanitize-coverage-allowlist=/dev/null'] )
+    add_global_arguments('-fsanitize-coverage-allowlist=instrumentation-filter',
                          native: false, language: ['c', 'cpp', 'objc'])
+  endif
 
   if get_option('fuzzing_engine') == ''
     # Add CFLAGS to tell clang to add fuzzer-related instrumentation to all the