hdf5-threadsafe: fix cmake flag, disable c++ api.

Short:
 - fix incorrect cmake flag `"-DDHDF5_ENABLE_THREADSAFE:BOOL=ON"` -> `"-DHDF5_ENABLE_THREADSAFE:BOOL=ON"`.
 - disable unsupported c++ api in hdf5-threadsafe.

Breaking:
Note: this bug means that historically nixpkgs was building hdf5-threadsafe without threadsafety enabled, but with c++ support.
C++ and threadsafe are unsupported, so this fix is a slight breaking change if downstream users were relying on hdf5-threadsafe exposing the c++ api.
If we instead want to expose both c++ and threadsafe, we would need "-DALLOW_UNSUPPORTED=ON", but then we are exposing a combination not supported or tested by upstream.

Related:
typo introduced in https://github.com/NixOS/nixpkgs/commit/cbd4d659e34c27cae5f48d7fdf6b2863f6492e6f
in the transition to cmake `"--enable-threadsafe"` was changed to `"-DDHDF5_ENABLE_THREADSAFE:BOOL=ON"`.
Note the double `D`, the correct syntax is `-DFLAG_NAME=VALUE`.

C++ was enabled by default in https://github.com/NixOS/nixpkgs/commit/9046690c73d913972e510566f03fad33fbe7eaf1

Longer:
```
$ nix build .#legacyPackages.aarch64-darwin.hdf5-threadsafe
$ nix log $(nix eval --raw .#legacyPackages.aarch64-darwin.hdf5-threadsafe.drvPath)
[...]
CMake Warning:
  Manually-specified variables were not used by the project:

    CMAKE_EXPORT_NO_PACKAGE_REGISTRY
    CMAKE_INSTALL_BINDIR
    CMAKE_INSTALL_DOCDIR
    CMAKE_INSTALL_INCLUDEDIR
    CMAKE_INSTALL_INFODIR
    CMAKE_INSTALL_LIBDIR
    CMAKE_INSTALL_LIBEXECDIR
    CMAKE_INSTALL_LOCALEDIR
    CMAKE_INSTALL_MANDIR
    CMAKE_INSTALL_SBINDIR
    CMAKE_POLICY_DEFAULT_CMP0025
    DHDF5_ENABLE_THREADSAFE

[...]
```

```
$ git grep -ni 'DHDF5_ENABLE_THREADSAFE'
pkgs/tools/misc/hdf5/default.nix:93:    "-DDHDF5_ENABLE_THREADSAFE:BOOL=ON"
```

We can see the correct version of this flag in the hdf5 repo
```
$ git grep -ni 'HDF5_ENABLE_THREADSAFE'
.github/workflows/arm-main-cmake.yml:94:            -DHDF5_ENABLE_THREADSAFE:BOOL=ON \
[...]
CMakeBuildOptions.cmake:59:option (HDF5_ENABLE_THREADSAFE "Enable thread-safety" OFF)
[...]
```

after this fix we can again inspect the cmake output, and we no longer see a warning for this unsupported variable

```
$ nix build .#legacyPackages.aarch64-darwin.hdf5-threadsafe
$ nix log $(nix eval --raw .#legacyPackages.aarch64-darwin.hdf5-threadsafe.drvPath)
[...]

CMake Warning:
  Manually-specified variables were not used by the project:

    CMAKE_EXPORT_NO_PACKAGE_REGISTRY
    CMAKE_INSTALL_BINDIR
    CMAKE_INSTALL_DOCDIR
    CMAKE_INSTALL_INCLUDEDIR
    CMAKE_INSTALL_INFODIR
    CMAKE_INSTALL_LIBDIR
    CMAKE_INSTALL_LIBEXECDIR
    CMAKE_INSTALL_LOCALEDIR
    CMAKE_INSTALL_MANDIR
    CMAKE_INSTALL_SBINDIR
    CMAKE_POLICY_DEFAULT_CMP0025

[...]
```

if we try to compile with both cppSupport and threadsafe we receive
```
> CMake Error at CMakeLists.txt:959 (message):
>    **** C++ and thread-safety options are not supported, override with ALLOW_UNSUPPORTED option ****
```

Testing:
Builds clean on aarch64-darwin and x86_64-linux.

0 files changed, 0 insertions, 0 deletions