[FileCheck] Factor some parsing checks out
Both callers of parseNumericVariableDefinition() perform the same extra
check that no character is found after the variable name. This patch
factors out this check into parseNumericVariableDefinition().
Reviewers: jhenderson, chandlerc, jdenny, probinson, grimar, arichardson, rnk
Subscribers: JonChesterfield, rogfer01, hfinkel, kristina, rnk, tra, arichardson, grimar, dblaikie, probinson, llvm-commits, hiraditya
Differential Revision: https://reviews.llvm.org/D64226