util: detect_os: add DETECT_OS_FUCHSIA and DETECT_OS_POSIX_LITE

Fuchsia is a microkernel-like OS.  It strategically implements
some POSIX and Unix APIs to promote software re-use.

It considers itself POSIX lite.

"In order to reduce the amount of source modification needed to
run on Fuchsia, Fuchsia offers a POSIX compatibility layer, POSIX
Lite, that this software can target. POSIX Lite is layered on
top of the underlying Fuchsia System ABI as a client library.

However, POSIX Lite is not a complete implementation of POSIX."

In the case of Fuchsia + src/util, these heavy-weight POSIX
functions shouldn't be used:

- file descriptors
- syslog.h
- signals
- process creation

To differentiate POSIX Lite, which Fuchsia and all heavy-weight
POSIX implementations support, add DETECT_OS_POSIX_LITE.

The use case is incrementally upstreaming functionality used in
downstream drivers (lavapipe, ..). Being in-tree for obvious
patches helps until the full driver can be merged.

Reviewed-by: Gurchetan Singh <gurchetansingh@chromium.org>
Reviewed-by: Eric Engestrom <eric@igalia.com>
Acked-by: Rob Clark <robdclark@chromium.org>
Part-of: <https://gitlab.freedesktop.org/mesa/mesa/-/merge_requests/29539>

src/util/detect_os.h

@@ -52,6 +52,11 @@
 #define DETECT_OS_POSIX 1
 #endif
 
+#if defined(__Fuchsia__)
+#define DETECT_OS_FUCHSIA 1
+#define DETECT_OS_POSIX_LITE 1
+#endif
+
 #if defined(__GNU__)
 #define DETECT_OS_HURD 1
 #define DETECT_OS_POSIX 1
@@ -111,6 +116,9 @@
 #ifndef DETECT_OS_HAIKU
 #define DETECT_OS_HAIKU 0
 #endif
+#ifndef DETECT_OS_FUCHSIA
+#define DETECT_OS_FUCHSIA 0
+#endif
 #ifndef DETECT_OS_HURD
 #define DETECT_OS_HURD 0
 #endif
@@ -129,6 +137,9 @@
 #ifndef DETECT_OS_POSIX
 #define DETECT_OS_POSIX 0
 #endif
+#ifndef DETECT_OS_POSIX_LITE
+#define DETECT_OS_POSIX_LITE DETECT_OS_POSIX
+#endif
 #ifndef DETECT_OS_WINDOWS
 #define DETECT_OS_WINDOWS 0
 #endif