[Bug #19592] Fix ext/Setup support

	After [1], using ext/Setup to link some, but not all extensions failed
	during linking. I did not know about this option, and had assumed that
	only `--with-static-linked-ext` builds can include statically linked
	extensions.

	Include the support code for statically linked extensions in all
	configurations like before [1]. Initialize the table lazily to minimize
	footprint on builds that have no statically linked extensions.

	[1]: 790cf4b6 "Fix autoload status of
	         statically linked extensions"
	---
	 load.c    | 28 +++++++++++++++++-----------
	 vm.c      |  3 ---
	 vm_core.h |  6 ------
	 3 files changed, 17 insertions(+), 20 deletions(-)