libbacktrace: declare getpagesize if necessary

Fixes https://gcc.gnu.org/PR95012.

config.h.in

@@ -12,6 +12,10 @@
 /* Define to 1 if you have the `clock_gettime' function. */
 #undef HAVE_CLOCK_GETTIME
 
+/* Define to 1 if you have the declaration of `getpagesize', and to 0 if you
+   don't. */
+#undef HAVE_DECL_GETPAGESIZE
+
 /* Define to 1 if you have the declaration of `strnlen', and to 0 if you
    don't. */
 #undef HAVE_DECL_STRNLEN

configure

@@ -12453,6 +12453,16 @@ fi
 cat >>confdefs.h <<_ACEOF
 #define HAVE_DECL_STRNLEN $ac_have_decl
 _ACEOF
+ac_fn_c_check_decl "$LINENO" "getpagesize" "ac_cv_have_decl_getpagesize" "$ac_includes_default"
+if test "x$ac_cv_have_decl_getpagesize" = xyes; then :
+  ac_have_decl=1
+else
+  ac_have_decl=0
+fi
+
+cat >>confdefs.h <<_ACEOF
+#define HAVE_DECL_GETPAGESIZE $ac_have_decl
+_ACEOF
 
 for ac_func in lstat readlink
 do :

configure.ac

@@ -383,7 +383,7 @@ if test "$have_fcntl" = "yes"; then
 	    [Define to 1 if you have the fcntl function])
 fi
 
-AC_CHECK_DECLS(strnlen)
+AC_CHECK_DECLS([strnlen, getpagesize])
 AC_CHECK_FUNCS(lstat readlink)
 
 # Check for getexecname function.

mmap.c

@@ -42,6 +42,10 @@ POSSIBILITY OF SUCH DAMAGE.  */
 #include "backtrace.h"
 #include "internal.h"
 
+#ifndef HAVE_DECL_GETPAGESIZE
+extern int getpagesize (void);
+#endif
+
 /* Memory allocation on systems that provide anonymous mmap.  This
    permits the backtrace functions to be invoked from a signal
    handler, assuming that mmap is async-signal safe.  */

mmapio.c

@@ -40,6 +40,10 @@ POSSIBILITY OF SUCH DAMAGE.  */
 #include "backtrace.h"
 #include "internal.h"
 
+#ifndef HAVE_DECL_GETPAGESIZE
+extern int getpagesize (void);
+#endif
+
 #ifndef MAP_FAILED
 #define MAP_FAILED ((void *)-1)
 #endif