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This is based off intial work by @jirislaby in #481. However it
has been substantially modified.
Notably it includes a separate build sytem to build the runtimes which
is inspired by the old build system. The reason for doing this is
because CMake is not well suited for building the runtime:
* CMake is configured to use the host compiler, not the bitcode
compiler. These are not the same thing.
* Building the runtime using `add_custom_command()` is flawed
because we can't automatically get transitive depencies (i.e.
header file dependencies) unless the CMake generator is makefiles.
(See `IMPLICIT_DEPENDS` of `add_custom_command()` in CMake).
So for now we have a very simple build system for building the runtimes.
In the future we can replace this with something more sophisticated if
we need it.
Support for all features of the old build system are implemented apart
from recording the git revision and showing it in the output of
`klee --help`.
Another notable change is the CMake build system works much better with
LLVM installs which don't ship with testing tools. The build system
will download the sources for `FileCheck` and `not` tools if the
corresponding binaries aren't available and will build them. However
`lit` (availabe via `pip install lit`) and GTest must already be
installed.
Apart from better support for testing a significant advantage of the
new CMake build system compared to the existing "Autoconf/Makefile"
build system is that it is **not** coupled to LLVM's build system
(unlike the existing build system). This means that LLVM's
autoconf/Makefiles don't need to be installed somewhere on the system.
Currently all tests pass.
Support has been implemented in TravisCI and the Dockerfile for
building with CMake.
The existing "Autoconf/Makefile" build system has been left intact
and so both build systems can coexist for a short while. We should
remove the old build system as soon as possible though because it
creates an unnecessary maintance burden.
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