BUILD: http: fix isdigit & isspace warnings on Solaris

As usual, when touching any is* function, Solaris complains about the
type of the element being checked. Better backport this to 1.5 since
nobody knows what the emitted code looks like since macros are used
instead of functions.
(cherry picked from commit 506c69a50e8d434b6b0c2c89b0402f220830644d)
1 file changed