[libc][semaphore] Zero-initialize rand_bytes to fix GCC warning (#195757)

GCC 15 warns about `rand_bytes` being maybe uninitialized when passed to
`getrandom`. Since `getrandom` writes to it, it doesn't strictly need
initialization, but zero-initializing it satisfies the compiler and
avoids the `-Werror=maybe-uninitialized` error.

Fix for https://github.com/llvm/llvm-project/pull/192278

Assisted by Gemini

libc/src/semaphore/linux/named_semaphore.cpp

diff --git a/libc/src/semaphore/linux/named_semaphore.cpp b/libc/src/semaphore/linux/named_semaphore.cpp
index 1c162ae..2dbd87c 100644
--- a/libc/src/semaphore/linux/named_semaphore.cpp
+++ b/libc/src/semaphore/linux/named_semaphore.cpp
@@ -61,7 +61,7 @@
 
 ErrorOr<TmpPath> generate_tmp_path() {
   // fill out 8 random bytes.
-  cpp::array<uint8_t, RANDOM_SUFFIX_BYTES> rand_bytes;
+  cpp::array<uint8_t, RANDOM_SUFFIX_BYTES> rand_bytes{};
   auto ret = linux_syscalls::getrandom(rand_bytes.data(), rand_bytes.size(), 0);
   if (!ret.has_value())
     return Error(ret.error());