[WebAssembly] Move .debug_line section address of dead function outside section range

Summary:
Currently we are pointing all debug information that refer removed function code
to the beginning of the code section (offset = 0). A debugger may want to
resolve code offset to the debug information, which will collide with offsets
of the live functions.

Moving offsets of dead functions outside code section range.

Reviewers: sbc100

Reviewed By: sbc100

Subscribers: dblaikie, ruiu, alexcrichton, dschuff, aprantl, jgravelle-google, aheejin, sunfish, JDevlieghere, llvm-commits

Differential Revision: https://reviews.llvm.org/D49446

llvm-svn: 342930