[libc] Disable epoll_pwait2 for now. (#99967)

This patch reverts #99781 and part of #99771 since `epoll_pwait2` is not
in fact available on all supported systems. It is my opinion that we
shouldn't provide a version of a function that doesn't perform as
expected, which is why this revert needs to happen.

The `epoll_pwait2` function can be reenabled when we have a way to check
if it is available on the target system, tracking bug for that is #80060

Author: michaelrj-google

libc/config/linux/riscv/entrypoints.txt

@@ -228,7 +228,9 @@ set(TARGET_LIBC_ENTRYPOINTS
     libc.src.sys.epoll.epoll_ctl
     libc.src.sys.epoll.epoll_pwait
     libc.src.sys.epoll.epoll_wait
-    libc.src.sys.epoll.epoll_pwait2
+    # TODO: Need to check if pwait2 is available before providing.
+    # https://github.com/llvm/llvm-project/issues/80060
+    # libc.src.sys.epoll.epoll_pwait2
 
     # sys/mman.h entrypoints
     libc.src.sys.mman.madvise

libc/config/linux/x86_64/entrypoints.txt

@@ -228,7 +228,9 @@ set(TARGET_LIBC_ENTRYPOINTS
     libc.src.sys.epoll.epoll_ctl
     libc.src.sys.epoll.epoll_pwait
     libc.src.sys.epoll.epoll_wait
-    libc.src.sys.epoll.epoll_pwait2
+    # TODO: Need to check if pwait2 is available before providing.
+    # https://github.com/llvm/llvm-project/issues/80060
+    # libc.src.sys.epoll.epoll_pwait2
 
     # sys/mman.h entrypoints
     libc.src.sys.mman.madvise

libc/src/sys/epoll/linux/epoll_pwait2.cpp

@@ -25,22 +25,10 @@ namespace LIBC_NAMESPACE_DECL {
 LLVM_LIBC_FUNCTION(int, epoll_pwait2,
                    (int epfd, struct epoll_event *events, int maxevents,
                     const struct timespec *timeout, const sigset_t *sigmask)) {
-#ifdef SYS_epoll_pwait2
   int ret = LIBC_NAMESPACE::syscall_impl<int>(
       SYS_epoll_pwait2, epfd, reinterpret_cast<long>(events), maxevents,
       reinterpret_cast<long>(timeout), reinterpret_cast<long>(sigmask),
       NSIG / 8);
-#elif defined(SYS_epoll_pwait)
-  // Convert nanoseconds to milliseconds, rounding up if there are remaining
-  // nanoseconds
-  long timeout_ms = static_cast<long>(timeout->tv_sec * 1000 +
-                                      (timeout->tv_nsec + 999999) / 1000000);
-  int ret = LIBC_NAMESPACE::syscall_impl<int>(
-      SYS_epoll_pwait, epfd, reinterpret_cast<long>(events), maxevents,
-      timeout_ms, reinterpret_cast<long>(sigmask), NSIG / 8);
-#else
-#error "epoll_pwait and epoll_pwait2 syscalls not available."
-#endif
 
   // A negative return value indicates an error with the magnitude of the
   // value being the error code.