Rework cmakery: (#136)

* Rework cmakery:
  * detect rocm/hip/rocshmem better, make sure that ROCM_PATH and
    ROCM_ROOT don't conflict and are taken by default
  * add /opt/rocm as a fallback when nothing else found
  * obtain hipcc in a sanitized way (ensure we use the same logic we
    use to later find_package hip)
  * factorize redundancies
  * export GPU_TARGETS as part of the cmake target for librocshmem,
    this helps with a clean error when an application tries to link
    with the wrong offload-target flag (rather than a cryptic link error)
  * phased out ROCSHMEM_HOME, in favor of rocshmem_ROOT (the cmake
    blessed way)

* Remove references to ROCSHMEM_HOME, we prefer ROCSHMEM_ROOT

* Pick CMAKE_PREFIX_PATH method for consistent finding hip/rocm

* Undo this pr using LANGUAGE HIP, maybe later

* Use only rocmcmakebuildtools as recommended from 6.4 onward

[ROCm/rocshmem commit: ee5363be7a]

projects/rocshmem/scripts/build_configs/ipc_tests_only

@@ -33,13 +33,10 @@ else
   install_path=$1
 fi
 
-if [ -z $1 ] && [ -z $ROCSHMEM_HOME ]
-then
-  export ROCSHMEM_HOME=/opt/rocm/
-fi
-
 src_path=$(dirname "$(realpath $0)")/../../
 
+# If as specific rocSHMEM version is required, the recommended approach
+# is to set environment variable 'rocshmem_ROOT'
 cmake \
     -DCMAKE_BUILD_TYPE=Release \
     -DCMAKE_INSTALL_PREFIX=$install_path \