i386: Use __seg_gs qualifiers in PTR_{MANGLE,DEMANGLE}() macros

i386: Use __seg_gs qualifiers in PTR_{MANGLE,DEMANGLE}() macros

Use __seg_gs named address space qualifiers in PTR_MANGLE() and
PTR_DEMANGLE() macros to access the pointer_guard field in the TCB.

This change allows the compiler to eliminate redundant reads of
the variable, reducing the number of reads from 105 to 94 and
decreasing the text size of the library by 280 bytes.

While at it, fix a few trivial whitespace issues as well

Signed-off-by: Uros Bizjak <ubizjak@gmail.com>
Reviewed-by: H.J. Lu <hjl.tools@gmail.com>