LLD is corrupting symbol tables again

[davidchisnall]

When we link a firmware image, objdump reports a load of missing files, something like:

/Users/theraven/llvm-project/Release/bin/llvm-objdump: warning: 'build/cheriot/cheriot/release/test-suite': failed to find source ISAType/../sdk/core/scheduler/main.cc
/Users/theraven/llvm-project/Release/bin/llvm-objdump: warning: 'build/cheriot/cheriot/release/test-suite': failed to find source ISAType/../sdk/core/scheduler/thread.h
/Users/theraven/llvm-project/Release/bin/llvm-objdump: warning: 'build/cheriot/cheriot/release/test-suite': failed to find source ISAType/../sdk/core/scheduler/timer.h
/Users/theraven/llvm-project/Release/bin/llvm-objdump: warning: 'build/cheriot/cheriot/release/test-suite': failed to find source ISAType/../sdk/core/scheduler/common.h

This is because the first part of the string is actually referring to a string table entry that's been deleted accidentally and so it is replaced with whichever string table entry is first.

A bug with the same symptoms was previously fixed

[resistor]

#132