[libunwind] Add missing alloca.h include

[ldionne]

Summary

At the moment we list a set of specifric platforms for which we use alloca for
_LIBUNWIND_REMEMBER_ALLOC. We assume that on those platforms alloca is already
provided somehow. This assumption turns out to be wrong sometimes. In
particular a baremetal system using picolibc is assumed to provide aloca, but
doesn't when compiled with pedantic/without gnu extentions.

This changes the behaviour by looking for different ways an alloca
implementation could be provided and using it when found. If no alloca can be
found we revert back to using malloc.

[mstorsjo]

alloca.h isn’t a standard header, and not all those platforms included in the ifdef do have a header with that name (even if they have the alloca function/macro provided somehow by some other header).

See earlier discussion in e.g. https://reviews.llvm.org/D149635.

[StevenvdSchoot]

In D154490#4473310, @mstorsjo wrote:

alloca.h isn’t a standard header, and not all those platforms included in the ifdef do have a header with that name (even if they have the alloca function/macro provided somehow by some other header).

See earlier discussion in e.g. https://reviews.llvm.org/D149635.

Ahh, sorry I missed that PR.
I see there has been no activity on that issue since May 10. Based on the comments there, I created a new version.

[mstorsjo]

libunwind/src/config.h

31

Please avoid changing the indentation of the otherwise unchanged lines (throughout the whole patch).

[StevenvdSchoot]

Undid formatting changes

[ldionne]

[Github PR transition cleanup]

Abandoning in favour of picking up D149635, where we suggested just using __builtin_alloca. All supported compilers should support it.

libunwind/src/config.h

 // Platform specific configuration defines.
 #ifdef __APPLE__
   #if defined(FOR_DYLD)
     #define _LIBUNWIND_SUPPORT_COMPACT_UNWIND 1
   #else
     #define _LIBUNWIND_SUPPORT_COMPACT_UNWIND 1
     #define _LIBUNWIND_SUPPORT_DWARF_UNWIND 1
   #endif
 #elif defined(_WIN32)
   #ifdef __SEH__
     #define _LIBUNWIND_SUPPORT_SEH_UNWIND 1
   #else
     #define _LIBUNWIND_SUPPORT_DWARF_UNWIND 1
   #endif
 #elif defined(_LIBUNWIND_IS_BAREMETAL)
   #if !defined(_LIBUNWIND_ARM_EHABI)
     #define _LIBUNWIND_SUPPORT_DWARF_UNWIND 1
#if defined(__i386__) || defined(__x86_64__) || defined(__powerpc__) ||        \
     (!defined(__APPLE__) && defined(__arm__)) || defined(__aarch64__) ||       \
     defined(__mips__) || defined(__riscv) || defined(__hexagon__) ||           \
     defined(__sparc__) || defined(__s390x__) || defined(__loongarch__)
 #if !defined(_LIBUNWIND_BUILD_SJLJ_APIS)
 #define _LIBUNWIND_BUILD_ZERO_COST_APIS
 #endif
 #endif
 
+#if defined(__has_builtin)
+#define _LIBUNWIND_HAS_BUILTIN(x) __has_builtin(x)
+#else
+#define _LIBUNWIND_HAS_BUILTIN(x) 0
+#endif
+
+#if defined(__has_include)
+#define _LIBUNWIND_HAS_INCLUDE(x) __has_include(x)
+#else
+#define _LIBUNWIND_HAS_INCLUDE(x) 0
+#endif
+
 #ifndef _LIBUNWIND_REMEMBER_HEAP_ALLOC
-#if defined(_LIBUNWIND_REMEMBER_STACK_ALLOC) || defined(__APPLE__) ||          \
-    defined(__linux__) || defined(__ANDROID__) || defined(__MINGW32__) ||      \
-    defined(_LIBUNWIND_IS_BAREMETAL)
+
+#if _LIBUNWIND_HAS_BUILTIN(__builtin_alloca)
+#define _LIBUNWIND_REMEMBER_ALLOC(_size) __builtin_alloca(_size)
+#define _LIBUNWIND_REMEMBER_FREE(_ptr)                                         \
+  do {                                                                         \
+  } while (0)
+#elif defined(alloca)
+#define _LIBUNWIND_REMEMBER_ALLOC(_size) alloca(_size)
+#define _LIBUNWIND_REMEMBER_FREE(_ptr)                                         \
+  do {                                                                         \
+  } while (0)
+#elif _LIBUNWIND_HAS_INCLUDE(<alloca.h>)
+#include <alloca.h>
 #define _LIBUNWIND_REMEMBER_ALLOC(_size) alloca(_size)
 #define _LIBUNWIND_REMEMBER_FREE(_ptr)                                         \
   do {                                                                         \
   } while (0)
 #elif defined(_WIN32)
 #define _LIBUNWIND_REMEMBER_ALLOC(_size) _malloca(_size)
 #define _LIBUNWIND_REMEMBER_FREE(_ptr) _freea(_ptr)
 #define _LIBUNWIND_REMEMBER_CLEANUP_NEEDED