Ignore gcc 10.3 'inline' warnings: 'call is unlikely and code size would grow'

As long as gcc does something with compatible semantics, it is up to gcc
how to optimize our code.

The alternative would be to export the functions in question from the
shared library, which has the disadvantage of greatly increasing the
number of calls across a shared library boundary.

Part-of: https://gitlab.freedesktop.org/dbus/dbus/-/merge_requests/275
Reviewed-by: Simon McVittie <smcv@collabora.com>

CMakeLists.txt

@@ -338,6 +338,7 @@ else()
         error=null-dereference
         error=strict-aliasing
         error=unused-parameter
+        inline
         unused-parameter
     )
     set(WARNINGS_ERRORS