Introduce `CMD_STRICT` to act as a parent for warnings about allowed but
disrecommended usage. Introduce a warning that discourages use of
non-target directives (which modify the build environment for the entire
[sub]tree). Add notes to the official documentation recommending use of
target-specific alternatives. This has been accepted wisdom for quite
some time, but only some of the affected commands made any mention of
this in the documentation.
This was left out of commit b7a5f2732d (PellesC: Add minimal support for
this C compiler, 2026-04-03) because the implementation was not usable
in general. It is now.
Closes: #21536
Co-authored-by: Serguei E. Leontiev <leo@sai.msu.ru>
The Pelles C compiler does not support ASM, and the `poasm` assembler
uses a distinct syntax. Add a dedicated language as we do for similar
cases from other vendors. Leave documentation commented out for now
because the PellesC toolchain support in general is not yet documented.
Fixes: #27758
Issue: #21536
Co-authored-by: Serguei E. Leontiev <leo@sai.msu.ru>
Try to be a bit more consistent about:
- Placing angle brackets around text which serves as a placeholder
rather than being literal.
- Using curly brackets rather than angle brackets to denote groups where
one of the options is required.
- Describing optional list arguments like `<x>...` rather than
`[<x>...]`. (Instances of lists not associated with keywords are
intentionally left as-is, however.)
Also, teach our CMake lexer to understand curly braces used as above
(prior uses were only in parsed literals without syntax highlighting),
and to highlight them (and remaining uses of angle braces) as the type
Punctuation rather than the type Operator, for consistency with square
braces.
