Add hexagon_benchmarks app for CMake builds

[prasmish]

This PR addresses the issue raised in #5374 regarding the lack of CMake support for hexagon_benchmark. Specifically, it introduces CMake build support for the hexagon_benchmark app which was previously missing.

During the process of adding this support, I observed that the sobel test was not building correctly with the target host-hvx. To keep this PR focused and manageable, the sobel test has been temporarily removed from this CMake script. A separate PR will be raised to rectify this issue and reintroduce the sobel test. (in #8127)

Fixes #8733

[steven-johnson]

Thanks so much for this fix! LGTM pending green.

[steven-johnson]

FAILED: hexagon_benchmarks/dilate3x3.generator 
: && /usr/bin/g++-9 -O3 -DNDEBUG -lc++abi hexagon_benchmarks/CMakeFiles/dilate3x3.generator.dir/dilate3x3_generator.cpp.o hexagon_benchmarks/CMakeFiles/dilate3x3.generator.dir/home/halidenightly/build_bot/worker/halide-testbranch-main-llvm17-x86-64-linux-cmake/halide-install/share/tools/GenGen.cpp.o -o hexagon_benchmarks/dilate3x3.generator  -Wl,-rpath,/home/halidenightly/build_bot/worker/halide-testbranch-main-llvm17-x86-64-linux-cmake/halide-install/lib  /home/halidenightly/build_bot/worker/halide-testbranch-main-llvm17-x86-64-linux-cmake/halide-install/lib/libHalide.so.18.0.0  -ldl && :
/usr/bin/ld: cannot find -lc++abi

[prasmish]

Earlier, I was building Halide with Clang, which led to a minor issue here. I’ve now eliminated an unneeded flag (-lc++abi) and now it should build smoothly.

[steven-johnson]

Failures are unrelated