Re-introduce the functionality to look for multiple iOS SDK versions

Currently, look for 12.1, 12.0 and 11.4. (But of course I recommend
people keep their Xcode updated, and thus now build against the 12.1
SDK.)

Also get rid of two AC_SUBST variables that were not used anywhere.

Change-Id: Ic1abf3eb1d900c843263dc781fd4c9a8ab126f09

config_host.mk.in

@@ -641,8 +641,6 @@ export WPG_CFLAGS=$(gb_SPACE)@WPG_CFLAGS@
 export WPG_LIBS=$(gb_SPACE)@WPG_LIBS@
 export WPS_CFLAGS=$(gb_SPACE)@WPS_CFLAGS@
 export WPS_LIBS=$(gb_SPACE)@WPS_LIBS@
-export IOS_SDK=@IOS_SDK@
-export IOS_DEPLOYMENT_VERSION=@IOS_DEPLOYMENT_VERSION@
 export XINERAMA_LINK=@XINERAMA_LINK@
 export XMLLINT=@XMLLINT@
 export XMLSEC_CFLAGS=$(gb_SPACE)@XMLSEC_CFLAGS@

configure.ac

@@ -2957,19 +2957,19 @@ dnl ===================================================================
 if test $_os = iOS; then
     AC_MSG_CHECKING([what iOS SDK to use])
     current_sdk_ver=12.1
+    older_sdk_vers="12.0 11.4"
     if test "$enable_ios_simulator" = "yes"; then
         platform=iPhoneSimulator
-        versionmin=-mios-simulator-version-min=$current_sdk_ver
+        versionmin=-mios-simulator-version-min=11.0
     else
         platform=iPhoneOS
         versionmin=-miphoneos-version-min=11.0
     fi
     xcode_developer=`xcode-select -print-path`
 
-    for sdkver in $current_sdk_ver; do
+    for sdkver in $current_sdk_ver $older_sdk_vers; do
         t=$xcode_developer/Platforms/$platform.platform/Developer/SDKs/$platform$sdkver.sdk
         if test -d $t; then
-            ios_sdk=$sdkver
             sysroot=$t
             break
         fi
@@ -2981,9 +2981,6 @@ if test $_os = iOS; then
 
     AC_MSG_RESULT($sysroot)
 
-    IOS_SDK=`echo $platform | tr A-Z a-z`$ios_sdk
-    IOS_DEPLOYMENT_VERSION=$current_sdk_ver
-
     # LTO is not really recommended for iOS builds,
     # the link time will be astronomical
     if test "$ENABLE_LTO" = TRUE; then
@@ -3003,9 +3000,6 @@ if test $_os = iOS; then
     RANLIB=`xcrun -find ranlib`
 fi
 
-AC_SUBST(IOS_SDK)
-AC_SUBST(IOS_DEPLOYMENT_VERSION)
-
 AC_MSG_CHECKING([whether to treat the installation as read-only])
 
 if test \( -z "$enable_readonly_installset" -a "$ENABLE_MACOSX_SANDBOX" = TRUE \) -o \