configure: Test if $make actually exists

configure doesn't detect if $make is installed on the build host.
This is also helpful for hosts where an alias for make is used, i.e.
configure would fail if gmake is not present on macOS.

Reviewed-by: Daniel P. Berrangé <berrange@redhat.com>
Signed-off-by: Roman Bolshakov <r.bolshakov@yadro.com>
Reviewed-by: Thomas Huth <thuth@redhat.com>
Message-Id: <20200825202755.50626-5-r.bolshakov@yadro.com>
Signed-off-by: Laurent Vivier <laurent@vivier.eu>

configure

@@ -1875,6 +1875,10 @@ if test -z "$python"
 then
     error_exit "Python not found. Use --python=/path/to/python"
 fi
+if ! has "$make"
+then
+    error_exit "GNU make ($make) not found"
+fi
 
 # Note that if the Python conditional here evaluates True we will exit
 # with status 1 which is a shell 'false' value.