[test] Fix ScalarEvolution test to allow __func__ with prototype

Fix ScalarEvolution/solve-quadratic.ll test to account for __func__
output listing the complete function prototype rather than just its
name, as it does on NetBSD.

Example Linux output:

  GetQuadraticEquation: addrec coeff bw: 4
  GetQuadraticEquation: equation -2x^2 + -2x + -4, coeff bw: 5, multiplied by 2

Example NetBSD output:

  llvm::Optional<std::tuple<llvm::APInt, llvm::APInt, llvm::APInt, llvm::APInt, unsigned int> > GetQuadraticEquation(const llvm::SCEVAddRecExpr*): addrec coeff bw: 4
  llvm::Optional<std::tuple<llvm::APInt, llvm::APInt, llvm::APInt, llvm::APInt, unsigned int> > GetQuadraticEquation(const llvm::SCEVAddRecExpr*): equation -2x^2 + -2x + -4, coeff bw: 5, multiplied by 2

Differential Revision: https://reviews.llvm.org/D55162

llvm-svn: 348096