Evaluate output section end symbol assignments in partial link

[parth-07]

Until now, the linker was not evaluating output section end symbol assignments in partial links. This commit fixes this behavior.

Resolves #479

[quic-seaswara]

This is a good start but I am not sure about what is its effect on symbol values that are specified in the output section.

cat > 1.c <<  \!
int foo(float x) { return 0; }
!

cat > s.t << \!
SECTIONS {
  .foo : {
    *(.text.foo)
    u1 = 0x100;
  }
}
!

/usr/bin/clang -c 1.c -ffunction-sections -fno-asynchronous-unwind-tables
#eld
ld.eld -r 1.o -o r.o -T s.t
readelf -s r.o | grep u1
ld.eld r.o -o out.eld && readelf -s out.eld | grep u1
#bfd
ld.bfd -r 1.o -o r.o -T s.t
readelf -s r.o | grep u1
ld.bfd r.o -o out.bfd && readelf -s out.bfd | grep u1
#lld
ld.lld -r 1.o -o r.o -T s.t
readelf -s r.o | grep u1
ld.lld r.o -o out.lld && readelf -s out.lld | grep u1

Please document this behavior.

[parth-07]

This is a good start but I am not sure about what is its effect on symbol values that are specified in the output section.

This patch does not affect the evaluations of symbol assignments that are specified in the output section. The above example shared behaves as expected, that is, the value of u1 is 0x100 with and without this patch changes.

Please document this behavior.

Symbol assignment evaluation order should be the same for both the usual and the partial link. We have the symbol assignment
evaluation order docs: https://qualcomm.github.io/eld/documentation/linker_script.html#assignment-evaluation-order. This patch makes the partial linking assignment evaluation order to what the docs states.