[sh4] Protect repatchCompact from flushConstantPool.

[sh4] Protect repatchCompact from flushConstantPool.
https://bugs.webkit.org/show_bug.cgi?id=124278

Patch by Julien Brianceau <jbriance@cisco.com> on 2013-11-13
Reviewed by Michael Saboff.

Random crashes may occur with sh4 architecture, when a flushConstantPool occurs in
movlMemRegCompact. As in this case a branch opcode and the constant pool are put
before the movlMemRegCompact, the branch itself is patched when calling repatchCompact
instead of the mov instruction, which is really bad.

* assembler/SH4Assembler.h:
(JSC::SH4Assembler::repatchCompact): Handle this specific case and add an ASSERT.

git-svn-id: http://svn.webkit.org/repository/webkit/trunk@159203 268f45cc-cd09-0410-ab3c-d52691b4dbfc