Remove blank from NaN string representation

Remove blank from NaN string representation

Flang front end function DumpHexadecimal generates a string
representation of a REAL value.  When the value is a NaN, the string
contains a blank, as in "NaN 0x7fc00000".  This function is used by
lowering to generate a string that is then passed to llvm Support
function convertFromStringSpecials, which does not expect a blank
in the string.  Remove the blank to allow correct recognition of a
NaN by this llvm function.

Note that function DumpHexadecimal is not exercised by the front end
itself.  This functionality is only exercised by code that is not yet
present in llvm.