semtimedop: fix timespec kernel ABI mismatch for 32-bit timeouts on x32

For time64 support, musl normally defines SYS_foo to the time32 variant
of that syscall on arches that have it, and to the time64 variant
otherwise, so that "SYS_foo == SYS_foo_time64" implies that the arch is
time64-only. However, SYS_semtimedop is an odd case: some arches define
only SYS_semtimedop_time64, yet they are not time64-only, because the
time32 variant is provided via SYS_ipc instead. For such arches,
defining SYS_semtimedop to SYS_semtimedop_time64 would break the
implication above, so commit 4bbd7baea7
doesn't do this. Commit eb2e298cdc
attempts to detect time64-only arches by checking that both
SYS_semtimedop and SYS_ipc are undefined, but this doesn't work for
x32, because it's a time64-only arch that does define SYS_semtimedop.
As a result, 32-bit timeouts trigger the fallback path that passes
a 32-bit timespec to the kernel while it expects a 64-bit one, so
the effective tv_sec is formed by interpreting 32-bit tv_sec and
tv_nsec as a single long long, and the effective tv_nsec is whatever
is located in the next 64 bits of the stack.

Fix this by expanding the time64-only check to include arches where
SYS_semtimedop is the time64 variant of the syscall.

src/ipc/semtimedop.c

@@ -7,7 +7,8 @@
 #define IS32BIT(x) !((x)+0x80000000ULL>>32)
 #define CLAMP(x) (int)(IS32BIT(x) ? (x) : 0x7fffffffU+((0ULL+(x))>>63))
 
-#if !defined(SYS_semtimedop) && !defined(SYS_ipc)
+#if !defined(SYS_semtimedop) && !defined(SYS_ipc) || \
+	SYS_semtimedop == SYS_semtimedop_time64
 #define NO_TIME32 1
 #else
 #define NO_TIME32 0