build: validate that system capstone works before using it

Some versions of capstone have shipped a broken pkg-config file which
puts the -I path without the trailing '/capstone' suffix. This breaks
the ability to "#include <capstone.h>". Upstream and most distros have
fixed this, but a few stragglers remain, notably FreeBSD.

Signed-off-by: Daniel P. Berrangé <berrange@redhat.com>
Signed-off-by: Alex Bennée <alex.bennee@linaro.org>
Reviewed-by: Thomas Huth <thuth@redhat.com>
Reviewed-by: Willian Rampazzo <willianr@redhat.com>
Reviewed-by: Richard Henderson <richard.henderson@linaro.org>
Message-Id: <20210625172211.451010-2-berrange@redhat.com>
Message-Id: <20210709143005.1554-7-alex.bennee@linaro.org>

meson.build

@@ -1657,6 +1657,19 @@ if capstone_opt in ['enabled', 'auto', 'system']
                         kwargs: static_kwargs, method: 'pkg-config',
                         required: capstone_opt == 'system' or
                                   capstone_opt == 'enabled' and not have_internal)
+
+  # Some versions of capstone have broken pkg-config file
+  # that reports a wrong -I path, causing the #include to
+  # fail later. If the system has such a broken version
+  # do not use it.
+  if capstone.found() and not cc.compiles('#include <capstone.h>',
+                                          dependencies: [capstone])
+    capstone = not_found
+    if capstone_opt == 'system'
+      error('system capstone requested, it does not appear to work')
+    endif
+  endif
+
   if capstone.found()
     capstone_opt = 'system'
   elif have_internal