cloudooo: Replace location by prefix

To avoid

[2020-06-03 15:35:15,590] INFO     While:
[2020-06-03 15:35:15,590] INFO       Installing.
[2020-06-03 15:35:15,590] INFO       Getting section template-cloudooo.
[2020-06-03 15:35:15,590] INFO       Initializing section
template-cloudooo.
[2020-06-03 15:35:15,591] INFO       Getting section
dynamic-template-cloudooo-instance-parameter-dict.
[2020-06-03 15:35:15,591] INFO       Initializing section
dynamic-template-cloudooo-instance-parameter-dict.
[2020-06-03 15:35:15,591] INFO       Getting option
dynamic-template-cloudooo-instance-parameter-dict:gcc.
[2020-06-03 15:35:15,591] INFO     Error: Referenced option does not
exist: gcc location

software/cloudooo/software-common.cfg

@@ -63,7 +63,7 @@ fontconfig-includes =
   ${fontconfig:location}/etc/fonts/conf.d
 
 freetype = ${freetype:location}
-gcc = ${gcc:location}
+gcc = ${gcc:prefix}
 glib = ${glib:location}
 glu = ${glu:location}
 haproxy = ${haproxy:location}