Bring back amxexec.obj temporarily

This file was last in c809ca2, and was
removed in 17e32a4.

Just bringing this back until we actually get rid of the ASM32 stuff
(which an assembler implementation of the amx interpreter -- these days the
C variant is preferred).

Author: qaisjp

amx-deps/src/.gitignore

@@ -352,3 +352,5 @@ healthchecksdb
 MigrationBackup/
 
 # End of https://www.gitignore.io/api/visualstudio
+
+!amx/amxexec.obj