fix bootstrap by renaming constexpr()

The addition of C23 keywords made 'constexpr'
unusable as a function name. This prevents cproc
from bootstrapping. This patch simply renames
the problematic function to 'evalexpr'.

README.md: Remove outdated note about gmake

Don't spam mailing list with build failures

Add a separate list for this.

Implement C23 predefined bool constants

Check object alignment in only one place

Move kind-specific decl fields to union

Keep track of asmname in decl and remove globalname()

Use new spelling of keywords in error messages

Add cproc(1) manual page

expr: Fix constant evaluation of struct member address

fb00ba6978 had the side-effect of introducing an integer to pointer
cast, which was not evaluated as a constant expression. To fix this,
just set the type of the expression.

Update qbe submodule

Use CC=cc with nixos

nixos doesn't have c99.

Add new C23 keywords

driver: Pass -iquote through to preprocessor

Update CI for new QBE Makefile

qbe: Insert dead block when compiling unreachable code after a jump

QBE will optimize out these blocks, and the dead block prevents the
possibility of NULL value usage when further control flow follows.

Fixes #80.

Fix tests for x86_64 -> x86_64-sysv target rename

Rename x86_64 target to include ABI

Add unreachable returns to silence compiler warnings

eval: Fix range check of double during conversion to int

2⁶⁴-1 and 2⁶³-1 are not representable as double and get rounded to
2⁶⁴ and 2⁶³ respectively, which are outside the range of 64-bit
[u]int.

This causes undefined behavior when a constant expression is evaluated
that involves a conversion of a very large or small value to an
integer type.

To fix this, change the > to >= and use constants representable as
double.