[gcc] Fix optimized expand of ptr diff for 64-bit PIC

SImode subtraction instructions use "m" contstraint for one operand and "i" constraint for another. This does not work in 64-bit PIC in nacl, as "i" allows symbol references which get rip-relative addressing.

This replaces "i" constraint with "e" contraint, where the latter does not allow symbol references except those that simply fit in 32-bits immediate.

Review URL: http://codereview.chromium.org/3187016
1 file changed