[InstCombine] Do not fold scalar ops over select with vector condition.

If OtherOpT or OtherOpF have scalar types and the condition is a vector,
we would create an invalid select.

Reviewers: spatel, john.brawn, mssimpso, craig.topper

Reviewed By: spatel

Differential Revision: https://reviews.llvm.org/D51781

llvm-svn: 341666