[llvm-exegesis] Adjust GLIBC_INITS_RSEQ condition

[MaskRay]

Summary

Commit 9f80831f3627e800709e2434bbbd5bb179b1576e introduced #include <sys/rseq.h>,
but RSEQ_SIG is only defined by some glibc ports (aarch64,arm,mips,powerpc,s390,x86),
causing other hosts (e.g., riscv64, loongarch64) to fail to build.

[MaskRay]

drop Compiler.h. For linux, gcc (2014) / clang have supported __has_include for very long time.

[aidengrossman]

This is definitely a much cleaner solution. Thanks for taking the time to write this up!

[xen0n]

LGTM from a cursory look. Thanks!

llvm/tools/llvm-exegesis/lib/BenchmarkRunner.cpp

 #include <perfmon/perf_event.h>
 #endif
 #include <sys/mman.h>
 #include <sys/ptrace.h>
 #include <sys/syscall.h>
 #include <sys/wait.h>
 #include <unistd.h>
 
-#ifdef __GLIBC__
-#if __GLIBC_MINOR__ >= 35
-#define GLIBC_INITS_RSEQ
-#endif // __GLIBC__MINOR > 35
-#endif // __GLIBC__
-
-#ifdef GLIBC_INITS_RSEQ
+#if defined(__GLIBC__) && __has_include(<sys/rseq.h>)
 #include <sys/rseq.h>
-#endif // HAS_RSEQ
-#endif // __linux__
+#ifdef RSEQ_SIG
+#define GLIBC_INITS_RSEQ
+#endif
+#endif
+#endif
 
 namespace llvm {
 namespace exegesis {
 
 BenchmarkRunner::BenchmarkRunner(const LLVMState &State, Benchmark::ModeE Mode,
                                  BenchmarkPhaseSelectorE BenchmarkPhaseSelector,
                                  ExecutionModeE ExecutionMode)
     : State(State), Mode(Mode), BenchmarkPhaseSelector(BenchmarkPhaseSelector),