Eliminating the use of quotes in cases where quotes aren't needed

In most cases we can just use the "if" statement's implicit variable dereferencing instead of using quotes.  In a single case, the "MSVC" variable is defined for visual studio on Windows, and so a string comparison can be elided completely.

- [x] MSVC with cmake 3.0
- [x] MSVC with cmake 3.1
- [x] libc++ with cmake 3.0
- [x] libc++ with cmake 3.1
- [x] libstdc++ with cmake 3.0
- [x] libstdc++ with cmake 3.1
- [x] gcc with cmake 3.0
- [x] gcc with cmake 3.1