complibs/cloog: add support for the ISL backend

CLooG 0.18+ will use ISL instead of PPL, so we have to configure
adequately depending of which backend is in use.

The Kconfig entries will decide for us which is selected, so we
can rely on either PPL xor ISL to be selected, not both.

Reported-by: "Plotnikov Dmitry" <leitz@ispras.ru>
[Dmitry did a preliminray patch to add ISL support,
which this patch is inspired from]
Signed-off-by: "Yann E. MORIN" <yann.morin.1998@free.fr>

CT_EXPERIMENTAL=y

CT_LOCAL_TARBALLS_DIR="${HOME}/src"

CT_SAVE_TARBALLS=y

CT_LOG_EXTRA=y

CT_ARCH_mips=y

CT_TARGET_VENDOR="malta"

CT_KERNEL_linux=y

CT_KERNEL_V_2_6_38=y

CT_BINUTILS_V_2_21_1a=y

CT_CC_V_4_4_6=y

# CT_CC_GCC_USE_GRAPHITE is not set

CT_LIBC_EGLIBC_V_2_13=y

CT_DEBUG_gdb=y

# CT_GDB_GDBSERVER_STATIC is not set

CT_GDB_V_7_2a=y

CT_GMP_V_5_0_1=y

CT_MPFR_V_3_0_0=y

CT_TEST_SUITE_GCC=y