Added the support of `gcc-ar`, `gcc-ranlib` and `gcc-nm`.

* compilers.jam: Added new rules, `get-ar`, `get-ranlib` and `get-nm`, in
                 order to provide correct values of `AR`, `RANLIB` and `NM`
                 environment variables in invocation of `configure` scripts.
                 They are required to handle LTO-enabled static libraries
                 created by GCC 4.8 or above.
* binutils/jamfile: Added `AR`, `RANLIB` and `NM` environment variables in
                    invocation of the `configure` script.
* clang/jamfile: Likewise.
* gmp/jamfile: Likewise.
* isl/jamfile: Likewise.
* cloog/jamfile: Likewise.
* gdb/jamfile: Likewise.
* icu4c/jamfile: Likewise.
* mpfr/jamfile: Likewise.
* mpc/jamfile: Likewise.
* opencv/jamfile: Likewise.
* openmpi/jamfile: Likewise.
* ppl/jamfile: Likewise.
* valgrind/jamfile: Likewise.
Merge branch 'master' into feature/gccAr
Added `*_FOR_TARGET` in building of Binutils and GDB.

* binutils/jamfile: Added `CC_FOR_TARGET`, `CXX_FOR_TARGET`,
                    `AR_FOR_TARGET`, `RANLIB_FOR_TARGET` and `NM_FOR_TARGET`
                    environment variables in building of GDB because both
                    host and target tools should be specified.
* gdb/jamfile: Likewise.
Merge pull request #102 from Cryolite/feature/gccAr

Added the support of `gcc-ar`, `gcc-ranlib` and `gcc-nm`.