C standard are all weak.
Apply __{BEGIN,END}_HIDDEN_DECLS to gdtoa{,imp}.h, hiding the
arch-specific __strtorx, __ULtox_D2A, __strtorQ, __ULtoQ_D2A symbols.
required by the C standard when called with an invalid base:
strtoll(), strtoimax(), strtoul(), strtoull(), and strtoumax().
Same behaviour for strtoq() and strtouq() even though not standardized.
No functional change in strtol(), it was the only one already correct.
While here, simplify the conditional expression for checking the base
and sync whitespace and comments among the six files.
ok millert@
guenther