[X86][fastcall][vectorcall] Move capability check before free register update

When passing arguments with `__fastcall` or `__vectorcall` in 32-bit MSVC, the following arguments have chance to be passed by register if the current one failed. `__regcall` from ICC is on the contrary: https://godbolt.org/z/4MPbzhaMG
All the three calling conversions are not supported in GCC.

Fixes: #57737

Reviewed By: rnk

Differential Revision: https://reviews.llvm.org/D133920