argp-standalone: include <alloca.h> under GCC (GCC 14+ / C23)

argp-parse.c and argp-help.c wrap the whole alloca-declaration block in
'#ifndef __GNUC__', so the header is never included when building with
GCC -- the code relied on GCC historically providing an implicit
declaration. GCC 14 promoted -Wimplicit-function-declaration to an error
and C23 removed implicit declarations, so the GCC 16 cross toolchain
fails:

  argp-parse.c:1227:36: error: implicit declaration of function 'alloca'
  argp-help.c:1329:35: error: implicit declaration of function 'alloca'

configure already sets HAVE_ALLOCA_H 1 and relibc's <alloca.h> defines
alloca(size) as __builtin_alloca(size), which is what GCC wants. Honour
HAVE_ALLOCA_H before consulting __GNUC__; non-GCC paths are untouched.

Patch generated by diff against pristine source, applies at --fuzz=0,
and the recipe cooks clean. Second opportunistic C23-era fix under the
gnu17 migration, after libiconv.

local/patches/argp-standalone/01-alloca-include-under-gcc.patch

@@ -0,0 +1,71 @@
+Include <alloca.h> under GCC too.
+
+Both argp-parse.c and argp-help.c wrap their entire alloca-declaration
+block in `#ifndef __GNUC__`, so the header is never included when
+compiling with GCC. That relied on GCC historically making `alloca`
+available through an implicit declaration.
+
+GCC 14 promoted -Wimplicit-function-declaration to an error, and C23
+removed implicit declarations outright, so on the GCC 16 cross toolchain
+the build fails:
+
+  argp-parse.c:1227:36: error: implicit declaration of function 'alloca'
+  argp-help.c:1329:35: error: implicit declaration of function 'alloca'
+
+configure already detects the header correctly (config.h defines
+HAVE_ALLOCA_H 1) and relibc's <alloca.h> defines
+`alloca(size) __builtin_alloca (size)`, which is exactly what GCC wants.
+The only defect is the __GNUC__ guard skipping the include.
+
+Honour HAVE_ALLOCA_H first; every non-GCC path is left untouched.
+
+--- a/argp-parse.c
++++ b/argp-parse.c
+@@ -27,6 +27,14 @@
+ #endif
+ 
+ /* AIX requires this to be the first thing in the file.  */
++/* Red Bear: honour HAVE_ALLOCA_H before consulting __GNUC__. The
++   original block is skipped entirely under GCC, which relied on GCC
++   implicitly declaring alloca. GCC 14 made implicit declarations an
++   error (C23 removed them), so GCC needs the real header too.
++   relibc's <alloca.h> defines alloca(size) as __builtin_alloca(size). */
++#if HAVE_ALLOCA_H
++#include <alloca.h>
++#else
+ #ifndef __GNUC__
+ #if HAVE_ALLOCA_H
+ #include <alloca.h>
+@@ -43,6 +51,7 @@
+ #endif
+ #endif
+ #endif
++#endif /* Red Bear: HAVE_ALLOCA_H */
+ 
+ #ifdef _WIN32
+ #include <windows.h>
+--- a/argp-help.c
++++ b/argp-help.c
+@@ -26,6 +26,14 @@
+ #endif
+ 
+ /* AIX requires this to be the first thing in the file.  */
++/* Red Bear: honour HAVE_ALLOCA_H before consulting __GNUC__. The
++   original block is skipped entirely under GCC, which relied on GCC
++   implicitly declaring alloca. GCC 14 made implicit declarations an
++   error (C23 removed them), so GCC needs the real header too.
++   relibc's <alloca.h> defines alloca(size) as __builtin_alloca(size). */
++#if HAVE_ALLOCA_H
++#include <alloca.h>
++#else
+ #ifndef __GNUC__
+ #if HAVE_ALLOCA_H || 0
+ #include <alloca.h>
+@@ -38,6 +46,7 @@
+ alloca();
+ #endif
+ #endif
++#endif /* Red Bear: HAVE_ALLOCA_H */
+ 
+ #include <stdbool.h>
+ #include <stddef.h>

recipes/wip/dev/other/argp-standalone/01-alloca-include-under-gcc.patch

@@ -0,0 +1 @@
+../../../../../local/patches/argp-standalone/01-alloca-include-under-gcc.patch

recipes/wip/dev/other/argp-standalone/recipe.toml

@@ -5,5 +5,8 @@ version = "0.1.0"
 [source]
 git = "https://github.com/argp-standalone/argp-standalone"
 shallow_clone = true
+patches = [
+    "01-alloca-include-under-gcc.patch"
+]
 [build]
 template = "meson"