[FileCheck] Fix FileCheck.cpp compilation on Solaris

[FileCheck] Fix FileCheck.cpp compilation on Solaris

Both LLVM 8.0.0 and current trunk fail to compile on Solaris with GCC 8.1.0:

  /vol/llvm/src/llvm/dist/utils/FileCheck/FileCheck.cpp: In function ‘void DumpAnnotatedInput(llvm::raw_ostream&, const llvm::FileCheckRequest&, llvm::StringRef, std::vector<InputAnnotation>&, unsigned int)’:
  /vol/llvm/src/llvm/dist/utils/FileCheck/FileCheck.cpp:408:41: error: call of overloaded ‘log10(unsigned int&)’ is ambiguous
     unsigned LineNoWidth = log10(LineCount) + 1;
                                           ^
  In file included from /vol/gcc-8/lib/gcc/i386-pc-solaris2.11/8.1.0/include-fixed/math.h:24,
                   from /vol/gcc-8/include/c++/8.1.0/cmath:45,
                   from /vol/llvm/src/llvm/dist/include/llvm-c/DataTypes.h:28,
                   from /vol/llvm/src/llvm/dist/include/llvm/Support/DataTypes.h:16,
                   from /vol/llvm/src/llvm/dist/include/llvm/ADT/Hashing.h:47,
                   from /vol/llvm/src/llvm/dist/include/llvm/ADT/ArrayRef.h:12,
                   from /vol/llvm/src/llvm/dist/include/llvm/Support/CommandLine.h:22,
                   from /vol/llvm/src/llvm/dist/utils/FileCheck/FileCheck.cpp:18:
  /vol/gcc-8/lib/gcc/i386-pc-solaris2.11/8.1.0/include-fixed/iso/math_iso.h:209:21: note: candidate: ‘long double std::log10(long double)’
    inline long double log10(long double __X) { return __log10l(__X); }
                       ^~~~~
  /vol/gcc-8/lib/gcc/i386-pc-solaris2.11/8.1.0/include-fixed/iso/math_iso.h:170:15: note: candidate: ‘float std::log10(float)’
    inline float log10(float __X) { return __log10f(__X); }
                 ^~~~~
  /vol/gcc-8/lib/gcc/i386-pc-solaris2.11/8.1.0/include-fixed/iso/math_iso.h:70:15: note: candidate: ‘double std::log10(double)’
   extern double log10 __P((double));
                 ^~~~~

Fixed by using std::log10 instead, which allowed the compilation on i386-pc-solaris2.11
and sparc-sun-solaris2.11 to continue.

Differential Revision: https://reviews.llvm.org/D60043

llvm-svn: 357509