Fix rts.cabal.in

Overlap with commit 2f463873, resulted in `hooks/LongGCSync.c`
missing from the `rts.cabal.in` file.  As the `rts.cabal` file is only
used by hadrian, this did not trigger with the make base build
system which can do globbing.

Also ignore the `rts.cabal` file, as it's generated by configure
from the `rts.cabal.in`.

.gitignore

@@ -166,6 +166,7 @@ _darcs/
 /mk/project.mk
 /mk/project.mk.old
 /mk/validate.mk
+/rts/rts.cabal
 /rts/package.conf.inplace
 /rts/package.conf.inplace.raw
 /rts/package.conf.install

rts/rts.cabal.in

@@ -379,6 +379,7 @@ library
                eventlog/EventLog.c
                eventlog/EventLogWriter.c
                hooks/FlagDefaults.c
+               hooks/LongGCSync.c
                hooks/MallocFail.c
                hooks/OnExit.c
                hooks/OutOfHeap.c