diy-mpich-3.5.0-bp156.2.1

- Add diy-glibc2.34-drop-SIGSTKSZ.patch to compile against glibc
  >= 2.34 which no longer defines SIGSTKSZ as constant
  (see, for instance, gh#catchorg/Catch2#2178).

- Add diy-include-stdexcept.patch: Include a missing header
  flagged by GCC 10; patch taken from upstream commit.

- Drop the "serial" flavour and build the no-mpi package for
  flavor = "".
- Fix build failures for openSUSE >= 1550 by not undefining
  "suffix" any more.
- Pass wrapped_mpi=ON to cmake to tell the build scripts that the
  MPI compiler wrapper requires no further MPI libraries; this
  fixes failing tests in %check.
- Use %cmake macro to configure; export compiler and env variables
  before calling cmake where possible instead of passing them as
  cmake options.

- Update to version 3.5.0
  * Release notes unavailable.
- Implement multibuild using mpich and serial flavours (others
  fail during %%check and are not recommended anyway).
- Implement %%check section.
- Disable all but x86_64: no other arch supported.
- Add diy-disable-memory-heavy-tests.patch: disable a few tests
  that are extremely memory expensive (>= 10 GB).

- Initial package.