Fix PR48742: the D75203 assembler optimization
locates MCRelaxableFragment's within two MCSymbol's and relaxes some
MCRelaxableFragment's to reduce the size of a MCAlignFragment.
A -g build has more MCSymbol's and therefore may have different assembler output
(e.g. a MCRelaxableFragment (jmp) may have 5 bytes with -O1 while 2 bytes with -O1 -g).
.p2align 4, 0x90 is common due to loops. For a larger program, with a
lot of temporary labels, the assembly output difference is somewhat
destined. The cost seems to overweigh the benefits so we default to
-x86-pad-for-align=false until the heuristic is improved.