Add getpwnam_r, getpwuid_r to emscripten (rust-lang#3906)

Author: ChanTsune

libc-test/semver/emscripten.txt

@@ -1,2 +1,4 @@
 getentropy
 posix_fallocate64
+getpwnam_r
+getpwuid_r

src/unix/linux_like/emscripten/mod.rs

@@ -1774,6 +1774,21 @@ extern "C" {
     ) -> ::c_int;
 
     pub fn getentropy(buf: *mut ::c_void, buflen: ::size_t) -> ::c_int;
+
+    pub fn getpwnam_r(
+        name: *const ::c_char,
+        pwd: *mut passwd,
+        buf: *mut ::c_char,
+        buflen: ::size_t,
+        result: *mut *mut passwd,
+    ) -> ::c_int;
+    pub fn getpwuid_r(
+        uid: ::uid_t,
+        pwd: *mut passwd,
+        buf: *mut ::c_char,
+        buflen: ::size_t,
+        result: *mut *mut passwd,
+    ) -> ::c_int;
 }
 
 // Alias <foo> to <foo>64 to mimic glibc's LFS64 support