Add sendfile to Glibc

Author: paulofaria

stdlib/public/Platform/glibc.modulemap.gyb

@@ -351,6 +351,10 @@ module SwiftGlibc [system] {
         header "${GLIBC_ARCH_INCLUDE_PATH}/sys/select.h"
         export *
       }
+      module sendfile {
+        header "${GLIBC_ARCH_INCLUDE_PATH}/sys/sendfile.h"
+        export *
+      }
       module socket {
         header "${GLIBC_ARCH_INCLUDE_PATH}/sys/socket.h"
         export *

validation-test/stdlib/Glibc.swift

@@ -24,6 +24,11 @@ GlibcTestSuite.test("errno") {
   expectEqual(EBADF, errno)
 }
 
+GlibcTestSuite.test("sendfile") {
+  // Check that `sendfile` is available.  Don't actually call it, because doing that is non-trivial.
+  expectEqual(((Int32, Int32, UnsafeMutablePointer<off_t>!, ssize_t) -> ssize_t).self, type(of: sendfile))
+}
+
 var GlibcIoctlConstants = TestSuite("GlibcIoctlConstants")
 
 GlibcIoctlConstants.test("tty ioctl constants availability") {