Added commended out use of -save-temps=obj

Whenever C++ source code contains device code, DPC++ would perform
two compilation passes (for host and for device portions) and combine
these two into fat object file. In the process of doing this it generates
temporary integration headers. So functions from these headers get
instrumented and .lcov file would contain references to deleted header
files, in the form of /tmp/dpctl_sycl_queue_integrface-header-hex.h

Added -save-temps instructs DPC++ to keep all the temporaries around and
makes these headers available for llvm-profdata and llvm-cov to use.

The side-effect of using -save-temps=obj is that preprocessor output
files are also kept around and referenced by instrumentation tools.
These files are very large. So much so that generated .json file can
not be uploaded to coverall service.

Therefore the -save-temps=obj is commented out. May still be useful
for manual profile collection.

References to deleted header files are still present (and wreck
llvm-lcov calls), but that can be addressed using llvm-cov option to
ignore certain files (like /tmp/dpctl_*.h)

Author: oleksandr-pavlyk

libsyclinterface/cmake/modules/SetupCoverage.cmake

@@ -11,6 +11,7 @@ function(setup_coverage_generation)
         "-fprofile-instr-generate "
         "-fcoverage-mapping "
         "-fno-sycl-use-footer "
+#        "-save-temps=obj "
         "-DDPCTL_COVERAGE "
     )