Only check for Linux-specific input APIs on Linux targets (thanks, Marcus!).

This is only for the configure script. The CMake project files already make
this Linux-exclusive.

Fixes Bugzilla #2659.

configure

@@ -23001,8 +23001,12 @@ case "$host" in
         CheckLibUDev
         CheckDBus
         CheckIBus
-        CheckInputEvents
-        CheckInputKD
+        case $ARCH in
+          linux)
+              CheckInputEvents
+              CheckInputKD
+          ;;
+        esac
         CheckTslib
         CheckUSBHID
         CheckPTHREAD

configure.in

@@ -2897,8 +2897,12 @@ case "$host" in
         CheckLibUDev
         CheckDBus
         CheckIBus
-        CheckInputEvents
-        CheckInputKD
+        case $ARCH in
+          linux)
+              CheckInputEvents
+              CheckInputKD
+          ;;
+        esac
         CheckTslib
         CheckUSBHID
         CheckPTHREAD