[Test] Fix undef var in catch-undef-behavior.c

[Test] Fix undef var in catch-undef-behavior.c

Commit 9e52c43090f8cd980167bbd2719878ae36bcf6b5 removed the directive
defining LINE_1600 but left a string substitution to that variable in a
CHECK-NOT directive. This will make that CHECK-NOT directive always fail
to match, no matter the string.

This commit follows the pattern done in
9e52c43090f8cd980167bbd2719878ae36bcf6b5 of simplifying the CHECK-NOT to
only look for the function name and the opening parenthesis, thereby not
requiring the LINE_1600 variable.

Reviewed By: rnk

Differential Revision: https://reviews.llvm.org/D93350