Fix FreeBSD/PowerPC* issues - #2147
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StacktracePowerPCGetLRPtr() falls back to OS checks when the compiler does not provide the _CALL_* ABI macros. Clang defines neither _CALL_SYSV nor _CALL_AIX on any FreeBSD PowerPC target (64-bit gets only _CALL_ELF=2), so 32-bit powerpc-*-freebsd hits the __FreeBSD__ fallback and reads the LR from sp[2]. The 32-bit SVR4 ABI saves the LR in the second word of the frame, sp[1]; sp[2] is correct only for the 64-bit ELF ABIs and Darwin/AIX. Verified against clang codegen: powerpc-unknown-freebsd emits "stwu 1,-16(1); stw 0,20(1)" (old SP + 4) while powerpc64-unknown-freebsd emits "stdu 1,-48(1); std 0,64(1)" (old SP + 16). Key the fallback on the word size instead of the OS: any __PPC64__ target uses sp[2], and 32-bit ELF targets (Linux, FreeBSD) use sp[1]. This is behavior-preserving for Linux and for 64-bit FreeBSD, and fixes the 32-bit FreeBSD case (currently latent, since stacktrace_config.h does not select this unwinder on FreeBSD).
The FreeBSD branch reads the kern.timecounter.tc.timebase.frequency sysctl straight into a double. The kernel registers that OID as CTLTYPE_U64 (sys/kern/kern_tc.c, tc_init()), so sysctlbyname() fills the 8-byte buffer with the integer 512000000 and the bits are then interpreted as an IEEE double: Frequency() returns ~2.5e-315 instead of 5.12e+08. The size check cannot catch this because uint64_t and double are both 8 bytes. Observed on FreeBSD 15.1 powerpc64le and powerpc64 (POWER9): - LOG_EVERY_N_SEC / VLOG_EVERY_N_SEC never rate-limit, because LogEveryNSecState::ShouldLog() computes the next log time as now + seconds * Frequency() ~= now (1000 of 1000 iterations logged with a 3600 s period). - Mutex waiters refresh their pthread_getschedparam() cache on every block instead of once per second. Read the sysctl into a uint64_t and convert to double; keep 0.0 if the sysctl fails.
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This is a cumulative PR for two FreeBSD/PowerPC* changes: