i386: Add _CET_ENDBR to indirect jump targets
cb9f0a2df822
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Description

i386: Add _CET_ENDBR to indirect jump targets

* mpi/i386/mpih-add1.S (_gcry_mpih_add_n): Save and restore
%ebx if IBT is enabed.  Add _CET_ENDBR to indirect jump targets
and adjust jump destination for _CET_ENDBR.
* mpi/i386/mpih-sub1.S (_gcry_mpih_sub_n): Likewise.

i386 mpih-add1.S and mpih-sub1.S use a trick to implment jump tables
with LEA. We can't use conditional branches nor normal jump tables
since jump table entries use EFLAGS set by jump table index. This
patch adds _CET_ENDBR to indirect jump targets and adjust destination
for _CET_ENDBR.