autotools: Require GNU sort

find_lib() uses sort -V, which is a GNU extension. Users of non-GNU
operating systems should either install GNU coreutils (assumed to
provide a gsort executable), or use the CMake build system.

Resolves: https://github.com/libsdl-org/SDL/issues/6106
Signed-off-by: Simon McVittie <smcv@collabora.com>
(cherry-picked from commit 732e1530e3ef48c225295e81fe84ed282eef3a39)

configure

@@ -723,6 +723,7 @@ ALLOCA
 CPP
 LIBTOOLLINKERTAG
 LINKER
+SORT
 PKG_CONFIG_LIBDIR
 PKG_CONFIG_PATH
 PKG_CONFIG
@@ -17897,6 +17898,59 @@ if  test -z "$AWK" ; then
     as_fn_error $? "*** awk not found, aborting" "$LINENO" 5
 fi
 
+for ac_prog in gsort sort
+do
+  # Extract the first word of "$ac_prog", so it can be a program name with args.
+set dummy $ac_prog; ac_word=$2
+{ printf "%s\n" "$as_me:${as_lineno-$LINENO}: checking for $ac_word" >&5
+printf %s "checking for $ac_word... " >&6; }
+if test ${ac_cv_prog_SORT+y}
+then :
+  printf %s "(cached) " >&6
+else $as_nop
+  if test -n "$SORT"; then
+  ac_cv_prog_SORT="$SORT" # Let the user override the test.
+else
+as_save_IFS=$IFS; IFS=$PATH_SEPARATOR
+for as_dir in $PATH
+do
+  IFS=$as_save_IFS
+  case $as_dir in #(((
+    '') as_dir=./ ;;
+    */) ;;
+    *) as_dir=$as_dir/ ;;
+  esac
+    for ac_exec_ext in '' $ac_executable_extensions; do
+  if as_fn_executable_p "$as_dir$ac_word$ac_exec_ext"; then
+    ac_cv_prog_SORT="$ac_prog"
+    printf "%s\n" "$as_me:${as_lineno-$LINENO}: found $as_dir$ac_word$ac_exec_ext" >&5
+    break 2
+  fi
+done
+  done
+IFS=$as_save_IFS
+
+fi
+fi
+SORT=$ac_cv_prog_SORT
+if test -n "$SORT"; then
+  { printf "%s\n" "$as_me:${as_lineno-$LINENO}: result: $SORT" >&5
+printf "%s\n" "$SORT" >&6; }
+else
+  { printf "%s\n" "$as_me:${as_lineno-$LINENO}: result: no" >&5
+printf "%s\n" "no" >&6; }
+fi
+
+
+  test -n "$SORT" && break
+done
+test -n "$SORT" || SORT="false"
+
+if ! "$SORT" -V </dev/null >/dev/null
+then :
+  as_fn_error $? "GNU sort(1) is required" "$LINENO" 5
+fi
+
 # Check whether --enable-largefile was given.
 if test ${enable_largefile+y}
 then :
@@ -18226,7 +18280,7 @@ find_lib()
         host_lib_path="/usr/$base_libdir /usr/local/$base_libdir"
     fi
     for path in $env_lib_path $gcc_bin_path $gcc_lib_path $host_lib_path; do
-        lib=`ls -- $path/$1 2>/dev/null | sed 's,.*/,,' | sort -V -r | $AWK 'BEGIN{FS="."}{ print NF, $0 }' | sort -n -s | sed 's,[0-9]* ,,' | head -1`
+        lib=`ls -- $path/$1 2>/dev/null | sed 's,.*/,,' | "$SORT" -V -r | $AWK 'BEGIN{FS="."}{ print NF, $0 }' | "$SORT" -n -s | sed 's,[0-9]* ,,' | head -1`
         if test x$lib != x; then
             echo $lib
             return

configure.ac

@@ -70,6 +70,9 @@ if [ test -z "$AWK" ]; then
     AC_MSG_ERROR([*** awk not found, aborting])
 fi
 
+AC_CHECK_PROGS([SORT], [gsort sort], [false])
+AS_IF([! "$SORT" -V </dev/null >/dev/null], [AC_MSG_ERROR([GNU sort(1) is required])])
+
 dnl 64-bit file offsets if possible unless --disable-largefile is specified
 AC_SYS_LARGEFILE
 
@@ -186,7 +189,7 @@ find_lib()
         host_lib_path="/usr/$base_libdir /usr/local/$base_libdir"
     fi
     for path in $env_lib_path $gcc_bin_path $gcc_lib_path $host_lib_path; do
-        lib=[`ls -- $path/$1 2>/dev/null | sed 's,.*/,,' | sort -V -r | $AWK 'BEGIN{FS="."}{ print NF, $0 }' | sort -n -s | sed 's,[0-9]* ,,' | head -1`]
+        lib=[`ls -- $path/$1 2>/dev/null | sed 's,.*/,,' | "$SORT" -V -r | $AWK 'BEGIN{FS="."}{ print NF, $0 }' | "$SORT" -n -s | sed 's,[0-9]* ,,' | head -1`]
         if test x$lib != x; then
             echo $lib
             return