For whatever reason, the previous way would inject backslashes into any path that has spaces.

When we are using ccache anyway, always add the flags to make clang
happy. Also, fix copy-paste error regarding what variable to modify for
it.

The official ccache documentation[1] recommends to set
`CMAKE_C(XX)_COMPILER_LAUNCHER` to ccache to enable ccache.
These also work as envionment variables (supported by CMake itself).
However, using these instructions generates the following error during
building:

    ccache: error: Recursive invocation (the name of the ccache binary must be "ccache")

This is because Dolphin adds an additional command ccache layer (ccache
ccache compiler ...).

This fixes that issue by checking for `CMAKE_C(XX)_COMPILER_LAUNCHER`
before inserting our own. Also, use `CMAKE_C(XX)_COMPILER_LAUNCHER`
to add ccache because the CMake docs discourages the use of
`RULE_LAUNCH_COMPILE` in favour of `CMAKE_C(XX)_COMPILER_LAUNCHER`.

[1]: https://github.com/ccache/ccache/wiki/CMake

ScmRevGen: Generate Info.plist files containing the current version

OpenBSD calls minizip-ng's .pc file minizip.pc
Others call   minizip-ng's .pc file minizip-ng.pc