Add probing code to Configure.pm to learn how the compiler does 'static inline'

The compiler probing framework is intended to be generic, and is based on the
approach used by Perl 5's Configure, but with the compiler and linker flags
derived from Configure.pl's own values, which should make it portable to Win32
as well as *nix.

The probing code for static inline is a direct port of the Perl 5 code written
by Andy Dougherty, applied to Perl 5 as commit 17a6c8e38505fd8d in July 2010.
Add a #define MVM_STATIC_INLINE to gen/config.h
Convert MVM_sc_{get,set}_{obj,stable}_sc to inline functions.

This requires moving the include of "gc/wb.h" earlier, as the inline functions
use the macro it declares within their bodies.
Convert sc_set_code, sc_set_code_list and sc_get_object_count to inline.
Convert MVM_SC_WB_OBJ and MVM_SC_WB_ST from macros to inline functions.
Convert MVM_sc_push_object() to an inline function.
Fix new Configure probe on MSVC.

Hopefully, without breaking things on other platforms.