Env. vars used only by THAPI are prefixed with `LTTNG_UST_`

[thilinarmtb]

There are some variables used in THAPI with LTTNG_UST_ prefix (like LTTNG_UST_OPENCL,
LTTNG_UST_CUDA, etc.) that are only used by THAPI (not lttng-ust). These should be
properly prefixed with an appropriate prefix which we can claim (like THAPI_).

(base) thilina@aurora-uan-0011:~/thapi/thapi> grep -Irn "LTTNG_UST_OPENCL" .
./backends/opencl/tracer_opencl_helpers.include.c:1183:  s = getenv("LTTNG_UST_OPENCL_LIBOPENCL");
./backends/opencl/tracer_opencl_helpers.include.c:1201:  s = getenv("LTTNG_UST_OPENCL_HOST_PROFILE");
./backends/opencl/tracer_opencl_helpers.include.c:1204:  s = getenv("LTTNG_UST_OPENCL_DUMP");
./backends/opencl/tracer_opencl_helpers.include.c:1207:  s = getenv("LTTNG_UST_OPENCL_DUMP_START");
./backends/opencl/tracer_opencl_helpers.include.c:1210:  s = getenv("LTTNG_UST_OPENCL_DUMP_END");
./backends/opencl/tracer_opencl_helpers.include.c:1214:  s = getenv("LTTNG_UST_OPENCL_VERBOSE");
./backends/opencl/tracer_opencl.sh.in:92:      export LTTNG_UST_OPENCL_HOST_PROFILE=1
./backends/opencl/tracer_opencl.sh.in:96:      export LTTNG_UST_OPENCL_DUMP=1
./backends/opencl/tracer_opencl.sh.in:100:      export LTTNG_UST_OPENCL_DUMP=1
./backends/opencl/tracer_opencl.sh.in:101:      export LTTNG_UST_OPENCL_DUMP_START=$1
./backends/opencl/tracer_opencl.sh.in:102:      export LTTNG_UST_OPENCL_DUMP_END=$1
./backends/opencl/tracer_opencl.sh.in:107:      export LTTNG_UST_OPENCL_DUMP=1
./backends/opencl/tracer_opencl.sh.in:108:      export LTTNG_UST_OPENCL_DUMP_START=$1
./backends/opencl/tracer_opencl.sh.in:113:      export LTTNG_UST_OPENCL_DUMP=1
./backends/opencl/tracer_opencl.sh.in:114:      export LTTNG_UST_OPENCL_DUMP_END=$1
./backends/opencl/tracer_opencl.sh.in:174:if [ ! -z "$LTTNG_UST_OPENCL_DUMP" ]; then
./backends/opencl/tracer_opencl.sh.in:177:if [ -z "$LTTNG_UST_OPENCL_LIBOPENCL" ]; then
./backends/opencl/tracer_opencl.sh.in:178:  LTTNG_UST_OPENCL_LIBOPENCL=$(whichlib64_head libOpenCL.so)
./backends/opencl/tracer_opencl.sh.in:179:  if [ -n "$LTTNG_UST_OPENCL_LIBOPENCL" ]; then
./backends/opencl/tracer_opencl.sh.in:180:    export LTTNG_UST_OPENCL_LIBOPENCL="$LTTNG_UST_OPENCL_LIBOPENCL"
./backends/opencl/tracer_opencl.sh.in:188:export LTTNG_UST_OPENCL_VERBOSE=1
(base) thilina@aurora-uan-0011:~/thapi/thapi> grep -Irn "LTTNG_UST_CUDA" .
./backends/cuda/tracer_cudart_helpers.include.c:10:  s = getenv("LTTNG_UST_CUDART_LIBCUDART");
./backends/cuda/tracer_cudart_helpers.include.c:29:  s = getenv("LTTNG_UST_CUDART_VERBOSE");
./backends/cuda/tracer_cuda.sh.in:75:      export LTTNG_UST_CUDA_PROFILE=1
./backends/cuda/tracer_cuda.sh.in:135:if [ -z "$LTTNG_UST_CUDA_LIBCUDA" ]; then
./backends/cuda/tracer_cuda.sh.in:136:  LTTNG_UST_CUDA_LIBCUDA=$(whichlib64_head libcuda.so)
./backends/cuda/tracer_cuda.sh.in:137:  if [ -n "$LTTNG_UST_CUDA_LIBCUDA" ]; then
./backends/cuda/tracer_cuda.sh.in:138:    export LTTNG_UST_CUDA_LIBCUDA="$LTTNG_UST_CUDA_LIBCUDA"
./backends/cuda/tracer_cuda.sh.in:146:export LTTNG_UST_CUDA_VERBOSE=1
./backends/cuda/tracer_cuda.sh.in:148:  if [ -z "$LTTNG_UST_CUDART_LIBCUDART" ]; then
./backends/cuda/tracer_cuda.sh.in:149:    LTTNG_UST_CUDART_LIBCUDART=$(whichlib64_head libcudart.so)
./backends/cuda/tracer_cuda.sh.in:150:    if [ -n "$LTTNG_UST_CUDART_LIBCUDART" ]; then
./backends/cuda/tracer_cuda.sh.in:151:      export LTTNG_UST_CUDART_LIBCUDART="$LTTNG_UST_CUDART_LIBCUDART"
./backends/cuda/tracer_cuda.sh.in:158:  export LTTNG_UST_CUDART_VERBOSE=1
./backends/cuda/tracer_cuda_helpers.include.c:498:  s = getenv("LTTNG_UST_CUDA_LIBCUDA");
./backends/cuda/tracer_cuda_helpers.include.c:516:  s = getenv("LTTNG_UST_CUDA_VERBOSE");
./backends/cuda/tracer_cuda_helpers.include.c:523:  s = getenv("LTTNG_UST_CUDA_PROFILE");
(base) thilina@aurora-uan-0011:~/thapi/thapi> grep -Irn "LTTNG_UST_MPI" .
./backends/mpi/tracer_mpi_helpers.include.c:10:  s = getenv("LTTNG_UST_MPI_LIBMPI");
./backends/mpi/tracer_mpi_helpers.include.c:28:  s = getenv("LTTNG_UST_MPI_VERBOSE");
./backends/mpi/tracer_mpi.sh.in:84:if [ -z "$LTTNG_UST_MPI_LIBMPI" ]; then
./backends/mpi/tracer_mpi.sh.in:85:  LTTNG_UST_MPI_LIBMPI=$(whichlib64_head libmpi.so)
./backends/mpi/tracer_mpi.sh.in:86:  if [ -n "$LTTNG_UST_MPI_LIBMPI" ]; then
./backends/mpi/tracer_mpi.sh.in:87:    export LTTNG_UST_MPI_LIBMPI="$LTTNG_UST_MPI_LIBMPI"
./backends/mpi/tracer_mpi.sh.in:95:export LTTNG_UST_MPI_VERBOSE=1