Add tests for sycl_external attribute

Author: schittir

clang/test/SemaSYCL/sycl-external-attr-grammar.cpp

@@ -0,0 +1,16 @@
+// RUN: %clang_cc1 -fsycl-is-device -fsyntax-only -verify %s
+
+// expected-warning@+1{{'sycl_external' attribute only applies to functions}}
+[[clang::sycl_external]] int a;
+
+
+// expected-warning@+2{{'sycl_external' attribute only applies to functions}}
+struct s {
+[[clang::sycl_external]] int b;
+};
+
+// FIXME: The first declaration of a function is required to have the attribute.
+// The attribute may be optionally present on subsequent declarations
+int foo(int c);
+
+[[clang::sycl_external]] void foo();

clang/test/SemaSYCL/sycl-external-attr-ignore.cpp

@@ -0,0 +1,12 @@
+// RUN: %clang_cc1 -fsyntax-only -verify %s
+
+// expected-warning@+1{{'sycl_external' attribute ignored}}
+[[clang::sycl_external]] void bar() {}
+
+// expected-warning@+1{{'sycl_external' attribute ignored}}
+[[clang::sycl_external]] int a;
+
+// expected-warning@+2{{'sycl_external' attribute ignored}}
+namespace not_sycl {
+[[clang::sycl_external]] void foo() {}
+}