The function will refuse to use a register class with fewer registers
than MinNumRegs. This can be used by clients to avoid accidentally
increase register pressure too much.
The default value of MinNumRegs=0 doesn't affect how constrainRegClass()
works.
git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@140339 91177308-0d34-0410-b5e6-96231b3b80d8