bpo-35059, libmpdec: Add missing EXTINLINE in mpdecimal.h (GH-10128)

Declare functions with EXTINLINE:

* mpd_del()
* mpd_uint_zero()
* mpd_qresize()
* mpd_qresize_zero()
* mpd_minalloc()

These functions are implemented with "inline" or "ALWAYS_INLINE", but
declared without inline which cause linker error on Visual Studio in
Debug mode when using /Ob1.
(cherry picked from commit 3b1cba37)
Co-authored-by: Victor Stinner <vstinner@redhat.com>

Modules/_decimal/libmpdec/mpdecimal.h

@@ -818,12 +818,12 @@ void *mpd_sh_alloc(mpd_size_t struct_size, mpd_size_t nmemb, mpd_size_t size);
 mpd_t *mpd_qnew(void);
 mpd_t *mpd_new(mpd_context_t *ctx);
 mpd_t *mpd_qnew_size(mpd_ssize_t size);
-void mpd_del(mpd_t *dec);
+EXTINLINE void mpd_del(mpd_t *dec);
 
-void mpd_uint_zero(mpd_uint_t *dest, mpd_size_t len);
-int mpd_qresize(mpd_t *result, mpd_ssize_t size, uint32_t *status);
-int mpd_qresize_zero(mpd_t *result, mpd_ssize_t size, uint32_t *status);
-void mpd_minalloc(mpd_t *result);
+EXTINLINE void mpd_uint_zero(mpd_uint_t *dest, mpd_size_t len);
+EXTINLINE int mpd_qresize(mpd_t *result, mpd_ssize_t size, uint32_t *status);
+EXTINLINE int mpd_qresize_zero(mpd_t *result, mpd_ssize_t size, uint32_t *status);
+EXTINLINE void mpd_minalloc(mpd_t *result);
 
 int mpd_resize(mpd_t *result, mpd_ssize_t size, mpd_context_t *ctx);
 int mpd_resize_zero(mpd_t *result, mpd_ssize_t size, mpd_context_t *ctx);