Boost build time of E-ACSL dependencies

This merge requests addresses issue #23 and suggests the following changes:

- Adopt portable implementation of gmp (called mini-gmp). 
- Switch between full GMP library and mini-gmp library via --enable-full-gmp option in configure. By default mini-gmp is chosen. 
- Reduce the size of GMP distribution shipped with E-ACSL


See merge request !72

distribution of the GMP library (mini-gmp) and the full GMP library at
build time

Adapt to trunk branch  feature/virgile/filecheck-result

(removal of field return_stmt)

See merge request !71

(removal of field return_stmt)

Feature/virgile/fix tests env

Seems to fix testing issues when running in internal mode

See merge request !68

- If FRAMAC_SHARE is not already set, either frama-c -print-share-path
  gives a correct result, and there's no need to set FRAMAC_SHARE in the
  first place, or it does not, and putting this result in FRAMAC_SHARE
  won't do any good.
- there's no need (and it seems to confuse Frama-C) to -add-path when in
  internal mode.

[tests] update oracles from frama-c (stdio.h and stdlib.h)



See merge request !67

[Makefile] Precise flags for test module compilation

Needed for changes introduced by frama-c/frama-c!930

See merge request !69

- Declare explicitely the presence of tests/print.ml
- Compile it as dependency of `ptest_config` rather than
  `E_ACSL_TESTS` (in the latter case, they might not be compiled when
  `ptests` is launched, because `ptests` is launched by
  `E_ACSL_DEFAULT_TESTS` which is itself a dependency of `E_ACSL_TESTS`).

Needed for changes introduced by frama-c/frama-c!930

Bugfixes in distribution and changes in tests

@signoles I have rebased and updated this merge request as it has diverged significantly. 

Changes:
- Bugfixes in E-ACSL distributions. There were issues with some of the paths and the test suite in the generated distribution was not working.
- Renamed `e-acsl-runtime` test directory to `runtime` and `e-acsl-reject` to `reject`. This is for consistency with other directories, such as `gmp`, `no-main` etc. This also makes the paths shorter. I think we have discussed these change a while ago. 
- Updated as per changes to build process (external libraries)
- Updates as per Boris' suggestions (variable namespace)




See merge request !55

    in Frama-C). Prefix library variables with EACSL prefix.

clean

[Makefile] Renamed e-acsl-runtime and e-acsl-reject test directories to runtime and reject respectively

Frama-C variables

contrib libraries

Stack traces for assertion failures

Related to issue #14 
Replaces !63

This merge request suggests a change that produces stack traces on assertion failures. Without this functionality it is difficult to investigate issues causing E-ACSL assertion failures: the previous design reported only line and file numbers where the assertions have failed and terminated executions using `exit(1)`. 

Changes made by this merge request:
- Added an interface for executing shell commands from within the C RTL (`e_acsl_shexec.h`). This interface is required for running `addr2line`, a `binutils` tool that translates addresses into line and file numbers.
- Added an interface to the GLIBC backtrace function so stack traces could be generated.
- Updated C RTL string header to add several support functions.
- Updated C RTL assert header to enable trace generation and also to raise abort signals rather than end the executions via `exit(1)`.

See merge request !66