Huh. I could've sworn we didn't. My mistake, it's there in src/backend/Makefile .
In that case I'll amend the patch to use semaphore guards.
(On a side note, systemtap's semaphore support is actually a massive pain. The way it's implemented in <sys/sdt.h> means that a single compilation unit may not use both probes.d style markers produced by the dtrace script and use regular DTRACE_PROBE(providername,probename) preprocessor macros. If it attempts to do so, the DTRACE_PROBE macros will emit inline asm that tries to reference probename_semaphore symbols that will not exist, resulting in linker errors or runtime link errors. But that's really a systemtap problem. Core PostgreSQL doesn't use any explicit DTRACE_PROBE(...), STAP_PROBE(...) etc.)