move notes about QNX to a separate platform support page

docs/markdown/Platform-notes.md

@@ -0,0 +1,46 @@
+---
+short-description: Notes and known issues for specific platforms
+...
+
+# Platform notes
+
+This page collects information that is specific to a platform or to a toolchain.
+
+## QNX
+
+Meson can detect and use `qcc` and `q++`, the C and C++ compiler drivers shipped with the QNX
+Software Development Platform (SDP).  For cross compilation, point the `[binaries]` section of
+the cross file at `qcc` and `q++`, including the required `-V` target selector, and set
+`system = 'qnx'` in `[host_machine]`:
+
+```ini
+[binaries]
+c = ['qcc', '-Vgcc_ntoaarch64le']
+cpp = ['q++', '-Vgcc_ntoaarch64le']
+
+[host_machine]
+system = 'qnx'
+cpu_family = 'aarch64'
+cpu = 'aarch64'
+endian = 'little'
+```
+
+The following limitations apply:
+
+1. ThinLTO incremental cache does not work.  `-Db_thinlto_cache=true` raises an error at
+   configure time, while `-Db_lto=true` is unaffected.
+2. Alternate linker selection is not supported.  Setting `c_ld` or `cpp_ld` (for example to
+   `lld` or `gold`) raises an error.
+3. If a header is deleted, stale entries remain in the dependency files, because `-MP` does not
+   emit phony header rules.  A clean build is needed to recover.
+4. There is no static sanitizer runtime, so `-static-libasan` is rejected and only the shared
+   runtime can be linked.
+5. The available sanitizers depend on the SDP version.  SDP 7.1 only provides `libubsan`, so
+   `-Db_sanitize=address` and `-Db_sanitize=leak` fail to link there.  SDP 8.0 adds asan and
+   lsan.  `-Db_sanitize=undefined` works on both, and tsan is not available on either.
+6. C++20 named modules do not work.  With SDP 8.0, `-fmodules-ts` compiles but silently ignores
+   `.cppm` and `.ixx` files.  With SDP 7.1, `-fmodules-ts` is rejected for C++ sources.  Plain
+   `-fmodules` is rejected on both.  This only affects projects that enable modules through
+   `cpp_args`.
+7. Relinking is avoided for unchanged shared libraries only on native QNX builds.  When
+   cross compiling to QNX, shared libraries are always relinked.

docs/markdown/snippets/qcc-support.md

@@ -1,30 +1,5 @@
 ## Added support for the QNX qcc/q++ compiler driver
 
-Meson can now detect and use `qcc` and `q++`, the C and C++ compiler drivers shipped with the QNX Software Development Platform (SDP), and recognizes QNX as a target platform.
-
-**Cross-compiling for QNX**
-
-Point a cross file's `[binaries]` section at qcc/q++ including the
-required `-V` target selector, and declare `system = 'qnx'` in
-`[host_machine]`, for example:
-
-```ini
-[binaries]
-c = ['qcc', '-Vgcc_ntoaarch64le']
-cpp = ['q++', '-Vgcc_ntoaarch64le']
-
-[host_machine]
-system = 'qnx'
-cpu_family = 'aarch64'
-cpu = 'aarch64'
-endian = 'little'
-```
-
-Known Issues:
-1. ThinLTO incremental cache doesn't work — -Db_thinlto_cache=true raises a clear error at configure time; plain -Db_lto=true is unaffected. -flto-incremental= is rejected outright by cc1.
-2. No alternate linker selection — c_ld/cpp_ld in a cross/native file (e.g. 'lld', 'gold') raises MesonException. qcc's driver never invokes a separate linker binary itself, and QNX documents no equivalent mechanism.
-3. Stale dependency-file entries after deleting a header — -MP's phony-header rules aren't emitted by this cc1, unlike stock gcc. Narrow, unfixed; only shows up as a missed rebuild until a clean build.
-4. No static sanitizer runtime — -static-libasan is rejected as unknown; only the shared sanitizer runtime can ever be linked.
-5. Sanitizer runtime availability is SDP-version-dependent — SDP 7.1 ships only libubsan (no asan/lsan/tsan at all), so -Db_sanitize=address/=leak fail to link there; SDP 8.0 adds asan/lsan (still no tsan on either SDP). =undefined works on both.
-6. C++20 named modules are broken, differently per SDP — SDP 8.0: -fmodules-ts compiles but silently no-ops on .cppm/.ixx files (no code-level fix possible — it's driver-level source-suffix dispatch before cc1plus ever runs). SDP 7.1: worse — -fmodules-ts itself is hard-rejected as unrecognized on any C++ source. Plain -fmodules is hard-rejected on both SDPs. Only bites a project that explicitly opts into modules via cpp_args.
-7. Symbol-extraction relink-avoidance only applies natively — the gnu_syms() optimization (skip relinking when a shared library's exported symbols haven't changed) only kicks in for a native/self-hosted QNX build; cross-compiling to QNX from another host (the SDP's primary use case) always falls back to unconditional relinking, same as before this work.
+Meson can now detect and use `qcc` and `q++`, the C and C++ compiler drivers shipped with the
+QNX Software Development Platform (SDP), and recognizes QNX as a target platform.  See
+[Platform notes](Platform-notes.md#qnx) for cross compilation setup and known limitations.

docs/sitemap.txt

@@ -77,6 +77,7 @@ index.md
 		Project-templates.md
 	@REFMAN_PLACEHOLDER@
 	Reference-tables.md
+	Platform-notes.md
 	Style-guide.md
 	Rewriter.md
 	FAQ.md