Fully initialize ev.data.
Fully initialize ev.data.

On Linux systems, ev.data is an 8-byte field, but this code
currently initializes only 4 bytes of the field, leaving the
trailing 4 bytes unininitialized. This causes memory safety tools
like Valgrind to complain.

This patch no longer explicitly initializes .data, ensuring that C
structure initialization will force the .data field to be zero
initialized. Manual checks of the compiled binary show that the
compiler correctly initializes the 4 bytes for u32 only once, so
this change incurs minimal overhead.

Signed-off-by: Daniel A. Steffen <bc823475b60dbcbd7be1bbdfe095b5f1939d5bd2@apple.com>

apple/swift-corelibs-libdispatch,apple/swift-corelibs-libdispatch,apple/swift-corelibs-libdispatch,apple/swift-corelibs-libdispatch