libsycl.so-gdb.py installed with wrong name in wrong directory

[cgleggett]

with 95ded99 libsycl.so-gdb.py is getting installed as
INST_DIR//SRC_DIR/sycl/xmethods/$<TARGET_FILE_NAME:sycl>-gdb.py

where INST_DIR is the value of CMAKE_INSTALL_PREFIX, SRC_DIR is the location of the llvm source, and $<TARGET_FILE_NAME:sycl> is actually that exact string.

this got messed up somewhere between bb73d92 and 95ded99

config.py options were --cuda --shared-libs -o . -t release --no-werror

[bader]

Installation script is located here: https://github.com/intel/llvm/blob/sycl/sycl/CMakeLists.txt#L211 and was recently modified by @alexbatashev.
@alexbatashev, could you take a look, please?

Additional note: I would refactor the cmake files and move the parts related to libsyc.so-gdb.py to https://github.com/intel/llvm/tree/sycl/sycl/xmethods.

Tagging @mihails-strasuns-intel to keep him in the loop.