Initial exposing of target platform in corradeConfigure.h.

Currently only NaCl newlib/glibc are indicated.
Added @partialsupport Doxygen command.
Utility: Directory listing flags have no effect in NaCl newlib.
PluginManager: dlopen() is not supported in NaCl newlib.

Thus only static plugins are supported there.
PKGBUILD alternatives for both NaCl newlib and glibc.
Use proper build dir name in original NaCl PKGBUILD.
FindCorrade.cmake: don't link to `dl` in NaCl newlib.

No such thing there.