Re: Segfault in jit tuple deforming on arm64 due to LLVM issue

I created a commitfest entry[1] to have the CI test the patch. There
was a failure in headerscheck and cpluspluscheck when the include of
SectionMemoryManager.h is checked[2]

In file included from /usr/include/llvm/ADT/SmallVector.h:18,
from /tmp/cirrus-ci-build/src/include/jit/SectionMemoryManager.h:23,
from /tmp/headerscheck.4b1i5C/test.c:2:
/usr/include/llvm/Support/type_traits.h:17:10: fatal error:
type_traits: No such file or directory
17 | #include <type_traits>

Since the SmallVector.h include type_traits, this file can't be
compiled with a C compiler so I've just excluded it from headerscheck.

Loosely related to headerscheck, running it locally was failing as it
couldn't find the <llvm-c/Core.h> file. This is because headerscheck
except llvm include files to be in /usr/include and don't rely on
llvm-config. I created a second patch to use the LLVM_CPPFLAGS as
extra flags when testing the src/include/jit/* files.

Lastly, I've used www.github.com instead of github.com link to stop
spamming the llvm-project's PR with reference to the commit every time
it is pushed somewhere (which seems to be the unofficial hack[3]).

[1] https://commitfest.postgresql.org/49/5220/
[2] https://cirrus-ci.com/task/4646639124611072?logs=headers_headerscheck#L42-L46
[3] https://github.com/orgs/community/discussions/23123#discussioncomment-3239240