The time complexity of getISDThunkSec() is O(|ISD->ThunkSections|).
When thunk section spacing is enabled, ISD->ThunkSections can be in the
scale of size(ISD)/getThunkSectionSpacing(). In one large powerpc64le
executable, this number for .text is 25980.
It is very slow if every created thunk in the current
InputSectionDescription goes through the whole array.
Sort relocations by offset and leverage this property to optimize it to O(1):
If a thunk is located before the current relocation offset, once it
can't be reached, any subsequent relocation can't reach this thunk,