[cmake] revise scalapackpp from-source build

[evaleev]

todo:

• switch to FetchContent
• only need to fetch scalpackpp, which automatically finds/fetches blacspp as needed: Bump blacspp + use new cmake modules wavefunction91/scalapackpp#11

[bimalgaudel]

@evaleev is this going to address the following issue?

Compile and install TA

#!/usr/bin/env sh
cmake \
    -B build \
    -D TA_ASSUMES_ASLR_DISABLED=ON \
    -D BUILD_SHARED_LIBS=ON \
    -D TA_BUILD_UNITTEST=ON \
    -D CMAKE_BUILD_TYPE=Release \
    -D CMAKE_INSTALL_PREFIX=${HOME}/opt/tiledarray \
    -D CMAKE_TOOLCHAIN_FILE=cmake/vg/toolchains/macos-clang-mpi-accelerate.cmake .

Configure sample program

#!/usr/bin/env sh
cmake \
      -B build \
      -D CMAKE_EXPORT_COMPILE_COMMANDS=ON \
      -D CMAKE_CXX_COMPILER=$(which clang++) \
      -D BUILD_SHARED_LIBS=ON \
      -D CMAKE_PREFIX_PATH=${HOME}/opt/tiledarray

Error:

CMake Error at /usr/local/Cellar/cmake/3.19.4/share/cmake/Modules/FindPackageHandleStandardArgs.cmake:218 (message):
  Could NOT find OpenMP_CXX (missing: OpenMP_CXX_FLAGS OpenMP_CXX_LIB_NAMES)
Call Stack (most recent call first):
  /usr/local/Cellar/cmake/3.19.4/share/cmake/Modules/FindPackageHandleStandardArgs.cmake:582 (_FPHSA_FAILURE_MESSAGE)
  /usr/local/Cellar/cmake/3.19.4/share/cmake/Modules/FindOpenMP.cmake:529 (find_package_handle_standard_args)
  /usr/local/Cellar/cmake/3.19.4/share/cmake/Modules/CMakeFindDependencyMacro.cmake:47 (find_package)
  /Users/gaudel/opt/tiledarray/lib/blaspp/blasppConfig.cmake:8 (find_dependency)
  /usr/local/Cellar/cmake/3.19.4/share/cmake/Modules/CMakeFindDependencyMacro.cmake:47 (find_package)
  /Users/gaudel/opt/tiledarray/lib/cmake/BTAS/btas-config.cmake:86 (find_dependency)
  /Users/gaudel/opt/tiledarray/lib/cmake/tiledarray/tiledarray-config.cmake:42 (find_package)
  CMakeLists.txt:10 (find_package)
-- Configuring incomplete, errors occurred!
See also "/Users/gaudel/scratch/cpp/build/CMakeFiles/CMakeOutput.log".
See also "/Users/gaudel/scratch/cpp/build/CMakeFiles/CMakeError.log".

[evaleev]

@bimalgaudel no, that is another issue due to broken handling of OpenMP in blaspp. When configuring TA set use_openmp=OFF to work around.

cc: @wavefunction91