For some reason, the default setting in all Toolchain.cmake
is:
```
set(CMAKE_FIND_ROOT_PATH_MODE_PROGRAM NEVER)
set(CMAKE_FIND_ROOT_PATH_MODE_LIBRARY BOTH)
set(CMAKE_FIND_ROOT_PATH_MODE_INCLUDE BOTH)
```
For cross-compilation, CMAKE_FIND_ROOT_PATH_MODE_PROGRAM=NEVER
makes sense (we only want to find executables in host system root),
but CMAKE_FIND_ROOT_PATH_MODE_LIBRARY/INCLUDE should be set
to ONLY, otherwise cmake may find libraries in host system root,
and try to link with incompatible libraries (instead of
cross-compilation sysroot).
Fixes#431.
Add a mechanism to construct a full cross-compiler environment using the
"crosstool-ng" cross-compiler building utility. This is implemented in
the new "common.crosstool" include, and augments the "dockcross/base"
base image.
Update Makefile to consolidate Dockerfile generation, notably the
"sed"-based inclusion directives.
Finally, employ all of this to generate a "linux-mips" 32-bit hard-float
MIPS cross-compiler Dockcross image.
