Clean up the build system properties and related code.

- Deduplicate getcompilerflags, getdependancies, getlinkerflags.
- Remove $NoPedantic (add -Wno-pedantic to $CompileFlags instead).
- Remove --enable-freebsd-ports-openssl and all related code (this
  will be replaced with --no-pkg-config=[name] in the future).
- Remove some unused build system properties.
- Remove support for caching third party include and library paths
  (can cause unexpected problems when they change).