Fix handling of PT_GNU_EH_FRAME.

The bias for the PT_GNU_EH_FRAME was using the paddr instead of vaddr.
This doesn't match the way the load bias is calculated, which always
use vaddr - offset, so change to use vaddr.

Found on an old x86 device that has a vdso that sets vaddr differently
from paddr.

Add a new offline test to catch this case and update the elf interface
unit tests.

Also, fix a small bug in the unwind_for_offline tool.

Bug: 142365899

Test: Unit tests pass.
Change-Id: I5f0bf062dd8ee45aa8553189ba493ec962e0b059
diff --git a/libunwindstack/Android.bp b/libunwindstack/Android.bp
index b0f3786..2573b1c 100644
--- a/libunwindstack/Android.bp
+++ b/libunwindstack/Android.bp
@@ -239,6 +239,7 @@
         "tests/files/offline/bad_eh_frame_hdr_arm64/*",
         "tests/files/offline/debug_frame_first_x86/*",
         "tests/files/offline/debug_frame_load_bias_arm/*",
+        "tests/files/offline/eh_frame_bias_x86/*",
         "tests/files/offline/eh_frame_hdr_begin_x86_64/*",
         "tests/files/offline/invalid_elf_offset_arm/*",
         "tests/files/offline/jit_debug_arm/*",