Handle regmasks in Thumb1RegisterInfo::saveScavengerRegister().
Handle regmasks in Thumb1RegisterInfo::saveScavengerRegister().

This function could have r12 live across a function call when compiling
thumb1 code.

The test case for this is not included because it is very long. It must
provoke emergency spilling near a function call. The behavior is
provoked by MultiSource/Applications/JM/lencod, and it triggers an
assertion in the scavenger.

<rdar://problem/10963642>

git-svn-id: 0ff597fd157e6f4fc38580e8d64ab130330d2411@151855 91177308-0d34-0410-b5e6-96231b3b80d8

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