Even after 13e2200fa426faffb62bdaf8b2f1f5699eee1511 (Solaris lacks
`femode_t`, too), the Solaris `flang` build is still broken:
```
/vol/llvm/src/llvm-project/local/flang/runtime/exceptions.cpp:87:5: error: static assertion failed due to requirement 'sizeof(fenv_t) <= sizeof(int) * 8': increase ieee_status_type size
87 | sizeof(fenv_t) <= sizeof(int) * _FORTRAN_RUNTIME_IEEE_FENV_T_EXTENT, | ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
/vol/llvm/src/llvm-project/local/flang/runtime/exceptions.cpp:87:20: note: expression evaluates to '200 <= 32'
87 | sizeof(fenv_t) <= sizeof(int) * _FORTRAN_RUNTIME_IEEE_FENV_T_EXTENT, | ~~~~~~~~~~~~~~~^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
```
This patch fixes this by removing the assertion.
Tested on `amd64-pc-solaris2.11` and `sparcv9-sun-solaris2.11`.
AIX does not have `femode_t` in `<cfenv>` header, removing the assert to
fix build failures
---------
Co-authored-by: Mark Danial <mark.danial@ibm.com>