Auto merge of #2947 - SteveLauC:euidaccess-and-eaccess, r=JohnTitor

add euidaccess and eaccess on gnu/musl linux

[man page for these two functions](https://man7.org/linux/man-pages/man3/euidaccess.3.html)

`uClibc` does not support them, so these two functions can not be put in `linux/mod.rs`.

Author: bors

libc-test/semver/linux-gnu.txt

@@ -649,3 +649,5 @@ timex
 utmpname
 utmpx
 utmpxname
+euidaccess
+eaccess

libc-test/semver/linux-musl.txt

@@ -48,3 +48,5 @@ process_vm_writev
 pwritev64
 reallocarray
 timex
+euidaccess
+eaccess

src/unix/linux_like/linux/gnu/mod.rs

@@ -1329,6 +1329,9 @@ extern "C" {
 
     pub fn memfd_create(name: *const ::c_char, flags: ::c_uint) -> ::c_int;
     pub fn mlock2(addr: *const ::c_void, len: ::size_t, flags: ::c_uint) -> ::c_int;
+
+    pub fn euidaccess(pathname: *const ::c_char, mode: ::c_int) -> ::c_int;
+    pub fn eaccess(pathname: *const ::c_char, mode: ::c_int) -> ::c_int;
 }
 
 extern "C" {

src/unix/linux_like/linux/musl/mod.rs

@@ -754,6 +754,9 @@ extern "C" {
     pub fn memfd_create(name: *const ::c_char, flags: ::c_uint) -> ::c_int;
     pub fn mlock2(addr: *const ::c_void, len: ::size_t, flags: ::c_uint) -> ::c_int;
     pub fn malloc_usable_size(ptr: *mut ::c_void) -> ::size_t;
+
+    pub fn euidaccess(pathname: *const ::c_char, mode: ::c_int) -> ::c_int;
+    pub fn eaccess(pathname: *const ::c_char, mode: ::c_int) -> ::c_int;
 }
 
 cfg_if! {