test: add an attribute test

Author: nkcsgexi

test/attr/spi_available.swift

@@ -0,0 +1,10 @@
+// RUN: %target-typecheck-verify-swift
+
+@_spi_available(*, deprecated, renamed: "another") // expected-error {{SPI available only supports introducing version on specific platform}}
+public class SPIClass1 {}
+
+@_spi_available(*, unavailable) // expected-error {{SPI available only supports introducing version on specific platform}}
+public class SPIClass2 {}
+
+@_spi_available(AlienPlatform 5.2, *) // expected-warning {{unrecognized platform name 'AlienPlatform'}}
+public class SPIClass3 {}