libc: add <sys/eventfd.h> and corresponding implementations.

Change-Id: Ide040884c456190226e580513099fdb8377e015b
diff --git a/libc/arch-arm/syscalls.mk b/libc/arch-arm/syscalls.mk
index c364d1c..ba78c18 100644
--- a/libc/arch-arm/syscalls.mk
+++ b/libc/arch-arm/syscalls.mk
@@ -172,5 +172,6 @@
 syscall_src += arch-arm/syscalls/inotify_add_watch.S
 syscall_src += arch-arm/syscalls/inotify_rm_watch.S
 syscall_src += arch-arm/syscalls/poll.S
+syscall_src += arch-arm/syscalls/eventfd.S
 syscall_src += arch-arm/syscalls/__set_tls.S
 syscall_src += arch-arm/syscalls/cacheflush.S
diff --git a/libc/arch-arm/syscalls/eventfd.S b/libc/arch-arm/syscalls/eventfd.S
new file mode 100644
index 0000000..8d2cce9
--- /dev/null
+++ b/libc/arch-arm/syscalls/eventfd.S
@@ -0,0 +1,19 @@
+/* autogenerated by gensyscalls.py */
+#include <sys/linux-syscalls.h>
+
+    .text
+    .type eventfd, #function
+    .globl eventfd
+    .align 4
+    .fnstart
+
+eventfd:
+    .save   {r4, r7}
+    stmfd   sp!, {r4, r7}
+    ldr     r7, =__NR_eventfd2
+    swi     #0
+    ldmfd   sp!, {r4, r7}
+    movs    r0, r0
+    bxpl    lr
+    b       __set_syscall_errno
+    .fnend