Bump the ABI version for Swift 3.0.

This was previously bumped to move from Swift 1.2 to 2.0.  Time for 3.0.

Note, unlike last time (136965d), the
CMakeLists.txt change already says 3.0 so that won't get changed here.

Author: cooperp

lib/IRGen/IRGenModule.h

@@ -310,7 +310,7 @@ class IRGenModuleDispatcher {
 class IRGenModule {
 public:
   // The ABI version of the Swift data generated by this file.
-  static const uint32_t swiftVersion = 3;
+  static const uint32_t swiftVersion = 4;
 
   ASTContext &Context;
   IRGenOptions &Opts;

test/IRGen/objc.swift

@@ -139,5 +139,5 @@ class WeakObjC {
 // CHECK:  i32 1, !"Objective-C Image Info Version", i32 0}
 // CHECK:  i32 1, !"Objective-C Image Info Section", !"__DATA, __objc_imageinfo, regular, no_dead_strip"}
 //   512 == (2 << 8).  2 is the Swift ABI version.
-// CHECK:  i32 4, !"Objective-C Garbage Collection", i32 768}
-// CHECK:  i32 1, !"Swift Version", i32 3}
+// CHECK:  i32 4, !"Objective-C Garbage Collection", i32 1024}
+// CHECK:  i32 1, !"Swift Version", i32 4}