Fixes a clang warning in suite/tests/linux/signal_racesys.c.
Changes two inline asm direct jumps to indirect in core/unix/signal.c to work around clang text relocations that have suddently appeared in recent clang versions.
However, clang is still marking libdynamorio.so as TEXTREL, so I'm disabling the TEXTREL check on libdynamorio.so for 32-bit release clang. I also add a check refusing to build an official package with clang until this is fixed.
Issue: #2632 (closed)