[mips] Always use _LARGEFILE_SOURCE / _FILE_OFFSET_BITS for building MIPS 32-bit
When MIPS 32-bit compiler-rt is building on 32-bit host or using 32-bit
DLLVM_HOST_TRIPLE the _LARGEFILE_SOURCE and the _FILE_OFFSET_BITS=64
macros defined by statements from the HandleLLVMOptions.cmake. In case
of building 32-bit libraries on 64-bit host using default host triple
these macros are not defined. As a result assertions check a consistency
between the struct_kernel_stat_sz constant and the struct_kernel_stat_sz
start to fail.
To resolve this problem and enable building both 32/64-bit versions
of MIPS compiler-rt libraries on 64-bit host at once always explicitly
define the _LARGEFILE_SOURCE and the _FILE_OFFSET_BITS=64 macros
for MIPS 32-bit.