And replace the default `-L-L<path>` LDC switches in the default config
accordingly.
The first advantage is for cross-compilation, where additional sections
should now mostly get away with overriding `lib-dirs` (and `rpath` if
need be) only; not just to specify the directory containing cross-
compiled druntime and Phobos, but also further dirs containing the C
libs. No need to override a whole `[post-]switches` array anymore just
to tweak the lib dirs.
The second advantage is that we can search these dirs for compiler-rt
libs instead of being limited to `<bin dir>/../lib<LIB_SUFFIX specified
in CMake command line>` or trying to guess distro-specific paths
=> easy-peasy for distros and users.
This isn't implemented yet.
Required for dmd-testsuite's compilable/json2.d.
Also fixes a bug regarding ConfigFile::path() with a null config file
path (e.g., when disabled explicitly via `-conf=`) - the
std::string(const char *) ctor segfaults for a null pointer arg,
whereas llvm::StringRef handles null pointers gracefully.
For switches to be appended after the user switches (or right before the
first `-run` switch).
The sections inherit it (as well as `switches`) from the `default` section
if it isn't overridden explicitly.
Fixes issue #2186.
libconfig++ is only a thin wrapper around libconfig. Because of the
use of exception handling this wrapper requires more memory than needed.
As we have our own wrapper (ConfigFile) just drop the C++ stuff.
1. Main include corresponding to .cpp file, if any.
2. DMD and LDC includes.
3. LLVM includes.
4. System includes.
Also updated a few include guards to match the default format.
