Auto merge of #2100 - TheDoctor314:gettid, r=JohnTitor

Add gettid() for Linux

Fixes #2076

libc-test/build.rs

@@ -2737,6 +2737,9 @@ fn test_linux(target: &str) {
             // assume it's a int instead.
             "getnameinfo" if uclibc => true,
 
+            // FIXME: This needs musl 1.2.2 or later.
+            "gettid" if musl => true,
+
             _ => false,
         }
     });

src/unix/linux_like/android/mod.rs

@@ -2809,6 +2809,8 @@ extern "C" {
     pub fn regfree(preg: *mut ::regex_t);
 
     pub fn android_set_abort_message(msg: *const ::c_char);
+
+    pub fn gettid() -> ::pid_t;
 }
 
 cfg_if! {

src/unix/linux_like/linux/mod.rs

@@ -3594,6 +3594,8 @@ extern "C" {
         outbytesleft: *mut ::size_t,
     ) -> ::size_t;
     pub fn iconv_close(cd: iconv_t) -> ::c_int;
+
+    pub fn gettid() -> ::pid_t;
 }
 
 cfg_if! {