[master] RFR: Jump/stub length failures in x86_64 release builds

[Aleksey Shipilev]

My CI reports many failures on `make bootcycle-images` on x86_64, but only in release modes:


#  Internal Error (macroAssembler_x86.hpp:120), pid=2457838, tid=2457856
#  guarantee(this->is8bit(imm8)) failed: Short forward jump exceeds 8-bit offset at <NULL>:0



#  Internal Error (vtableStubs.cpp:196), pid=1871037, tid=1871042
#  guarantee(masm->pc() <= s->code_end()) failed: itable #2: overflowed buffer, estimated len: 256, actual len: 295, overrun: 39



#  Internal Error (vtableStubs.cpp:196), pid=1871037, tid=1871042
#  guarantee(masm->pc() <= s->code_end()) failed: itable #2: overflowed buffer, estimated len: 256, actual len: 295, overrun: 39


Additional testing:
 - [x] Linux x86_64 release `make bootcycle-images` now works

-------------

Commit messages:
 - Fix

Changes: https://git.openjdk.java.net/lilliput/pull/22/files
 Webrev: https://webrevs.openjdk.java.net/?repo=lilliput&pr=22&range=00
  Stats: 7 lines in 2 files changed: 1 ins; 4 del; 2 mod
  Patch: https://git.openjdk.java.net/lilliput/pull/22.diff
  Fetch: git fetch https://git.openjdk.java.net/lilliput pull/22/head:pull/22

PR: https://git.openjdk.java.net/lilliput/pull/22