add epoll to headers for other linux targets

I forgot to do this when I was adding the entrypoints.

Author: michaelrj-google

libc/config/linux/aarch64/headers.txt

@@ -24,4 +24,5 @@ set(TARGET_PUBLIC_HEADERS
     libc.include.unistd
 
     libc.include.sys_ioctl
+    libc.include.sys_epoll
 )

libc/config/linux/arm/headers.txt

@@ -9,4 +9,6 @@ set(TARGET_PUBLIC_HEADERS
     libc.include.string
     libc.include.strings
     libc.include.search
+
+    libc.include.sys_epoll
 )

libc/config/linux/riscv/headers.txt

@@ -29,6 +29,7 @@ set(TARGET_PUBLIC_HEADERS
     libc.include.arpa_inet
 
     libc.include.sys_auxv
+    libc.include.sys_epoll
     libc.include.sys_ioctl
     libc.include.sys_mman
     libc.include.sys_prctl