[llvm_mode] Work around segfault bug with clang custom passes (#18)
[llvm_mode] Work around segfault bug with clang custom passes (#18)

When shutting down LLVM, the custom pass shared library can be prematurely unloaded, resulting in a dangling pointer. As a workaround, instruct the linker to mark the custom pass not to be unloaded at runtime.

References:
https://groups.google.com/forum/#!msg/afl-users/TDLrTu3V_Pw/K4svutarAAAJ
https://stackoverflow.com/questions/47712670/segmentation-fault-in-llvm-pass-when-using-registerstandardpasses

Upstream bugs:
https://bugs.llvm.org/show_bug.cgi?id=34573
https://bugs.llvm.org/show_bug.cgi?id=39321
https://bugs.llvm.org/show_bug.cgi?id=36183
google/AFL,google/AFL,google/AFL,google/AFL,google/AFL