silence a couple of -Wqual-cast warning from GCC (NFC)

Cast to `const uint8_t *` instead of `uint8_t *` to avoid the warning
from GCC.

  EmulationStateARM.cpp:206:34: warning: cast from type 'const void*' to type 'uint8_t* {aka unsigned char*}' casts away qualifiers [-Wcast-qual]

Cast to `const uint32_t *` and the explicitly cast away the const-ness
of the value.  This seems pretty sketchy as the `DataExtractor` holds a
const reference to the data.  However, this is no worse than before.

  ObjectFilePECOFF.cpp:540:78: warning: cast from type 'const uint8_t* {aka const unsigned char*}' to type 'uint32_t* {aka unsigned int*}' casts away qualifiers [-Wcast-qual]

llvm-svn: 308489