Improve error messages if configure build test fails under macOS

Telling people to try using a different SDK was rather confusing if they
didn't specify any SDK in the first place and not very helpful if the
problem was due to specifying an incompatible minimum OS version, so fix
both problems at once by using the appropriate error message depending
on the configure options actually used.

configure

@@ -1028,7 +1028,6 @@ infodir
 docdir
 oldincludedir
 includedir
-runstatedir
 localstatedir
 sharedstatedir
 sysconfdir
@@ -1455,7 +1454,6 @@ datadir='${datarootdir}'
 sysconfdir='${prefix}/etc'
 sharedstatedir='${prefix}/com'
 localstatedir='${prefix}/var'
-runstatedir='${localstatedir}/run'
 includedir='${prefix}/include'
 oldincludedir='/usr/include'
 docdir='${datarootdir}/doc/${PACKAGE_TARNAME}'
@@ -1708,15 +1706,6 @@ do
   | -silent | --silent | --silen | --sile | --sil)
     silent=yes ;;
 
-  -runstatedir | --runstatedir | --runstatedi | --runstated \
-  | --runstate | --runstat | --runsta | --runst | --runs \
-  | --run | --ru | --r)
-    ac_prev=runstatedir ;;
-  -runstatedir=* | --runstatedir=* | --runstatedi=* | --runstated=* \
-  | --runstate=* | --runstat=* | --runsta=* | --runst=* | --runs=* \
-  | --run=* | --ru=* | --r=*)
-    runstatedir=$ac_optarg ;;
-
   -sbindir | --sbindir | --sbindi | --sbind | --sbin | --sbi | --sb)
     ac_prev=sbindir ;;
   -sbindir=* | --sbindir=* | --sbindi=* | --sbind=* | --sbin=* \
@@ -1854,7 +1843,7 @@ fi
 for ac_var in	exec_prefix prefix bindir sbindir libexecdir datarootdir \
 		datadir sysconfdir sharedstatedir localstatedir includedir \
 		oldincludedir docdir infodir htmldir dvidir pdfdir psdir \
-		libdir localedir mandir runstatedir
+		libdir localedir mandir
 do
   eval ac_val=\$$ac_var
   # Remove trailing slashes.
@@ -2007,7 +1996,6 @@ Fine tuning of the installation directories:
   --sysconfdir=DIR        read-only single-machine data [PREFIX/etc]
   --sharedstatedir=DIR    modifiable architecture-independent data [PREFIX/com]
   --localstatedir=DIR     modifiable single-machine data [PREFIX/var]
-  --runstatedir=DIR       modifiable per-process data [LOCALSTATEDIR/run]
   --libdir=DIR            object code libraries [EPREFIX/lib]
   --includedir=DIR        C header files [PREFIX/include]
   --oldincludedir=DIR     C header files for non-gcc [/usr/include]
@@ -18650,6 +18638,8 @@ if test "x$wxUSE_MACOSX_SDK" = "xno"; then
     wxUSE_MACOSX_SDK=
 elif test "x$wxUSE_MACOSX_SDK" = "xyes"; then
         wxUSE_MACOSX_SDK="`xcode-select -p`/Platforms/MacOSX.platform/Developer/SDKs/MacOSX.sdk"
+elif test "x$wxUSE_MACOSX_SDK" != "x"; then
+    macosx_sdk_specified=yes
 fi
 
 
@@ -18700,6 +18690,8 @@ $as_echo "$as_me: WARNING: Could not determine deployment target from SDKSetting
     fi
 elif test "x$wxUSE_MACOSX_VERSION_MIN" = "x"; then
     wxUSE_MACOSX_VERSION_MIN=10.10
+else
+    macosx_minver_specified=yes
 fi
 
 if test "x$MACOSX_SDK_OPTS" != "x"; then
@@ -18728,6 +18720,14 @@ if test "$HAVE_CXX11" = "1" ; then
 fi
 
 if test "x$retest_macosx_linking" = "xyes"; then
+    if test "x$macosx_sdk_specified" = "xyes"; then
+        error_message="no, try using a different SDK or using the default one."
+    elif test "x$macosx_minver_specified" = "xyes"; then
+        error_message="no, try using a different min OS version or omitting it."
+    else
+        error_message="no, check that Xcode command line tools are installed."
+    fi
+
     ac_ext=c
 ac_cpp='$CPP $CPPFLAGS'
 ac_compile='$CC -c $CFLAGS $CPPFLAGS conftest.$ac_ext >&5'
@@ -18751,10 +18751,7 @@ if ac_fn_c_try_link "$LINENO"; then :
   { $as_echo "$as_me:${as_lineno-$LINENO}: result: yes" >&5
 $as_echo "yes" >&6; }
 else
-  { { $as_echo "$as_me:${as_lineno-$LINENO}: error: in \`$ac_pwd':" >&5
-$as_echo "$as_me: error: in \`$ac_pwd':" >&2;}
-as_fn_error $? "no.  Try a different SDK
-See \`config.log' for more details" "$LINENO" 5; }; exit 1
+  as_fn_error $? "$error_message" "$LINENO" 5
 fi
 rm -f core conftest.err conftest.$ac_objext \
     conftest$ac_exeext conftest.$ac_ext
@@ -18788,10 +18785,7 @@ if ac_fn_cxx_try_link "$LINENO"; then :
   { $as_echo "$as_me:${as_lineno-$LINENO}: result: yes" >&5
 $as_echo "yes" >&6; }
 else
-  { { $as_echo "$as_me:${as_lineno-$LINENO}: error: in \`$ac_pwd':" >&5
-$as_echo "$as_me: error: in \`$ac_pwd':" >&2;}
-as_fn_error $? "no.  Try a different SDK
-See \`config.log' for more details" "$LINENO" 5; }; exit 1
+  as_fn_error $? "$error_message" "$LINENO" 5
 fi
 rm -f core conftest.err conftest.$ac_objext \
     conftest$ac_exeext conftest.$ac_ext