[ModuleInterface] Change swift-tools-version to swift-compiler-version (#25160)

swift-tools-version as used by SwiftPM is an actual, parsed field with
semantic meaning. swift-compiler-version as used when generating
module interfaces is just to record what version of the compiler
generated the interface. They shouldn't have the same name.

Author: jrose-apple

include/swift/Frontend/ParseableInterfaceSupport.h

@@ -18,7 +18,7 @@
 #include "llvm/Support/Regex.h"
 
 #define SWIFT_INTERFACE_FORMAT_VERSION_KEY "swift-interface-format-version"
-#define SWIFT_TOOLS_VERSION_KEY "swift-tools-version"
+#define SWIFT_COMPILER_VERSION_KEY "swift-compiler-version"
 #define SWIFT_MODULE_FLAGS_KEY "swift-module-flags"
 
 namespace swift {

lib/Frontend/ParseableInterfaceSupport.cpp

@@ -66,7 +66,7 @@ static void printToolVersionAndFlagsComment(raw_ostream &out,
       Ctx.LangOpts.EffectiveLanguageVersion);
   out << "// " SWIFT_INTERFACE_FORMAT_VERSION_KEY ": "
       << InterfaceFormatVersion << "\n";
-  out << "// " SWIFT_TOOLS_VERSION_KEY ": "
+  out << "// " SWIFT_COMPILER_VERSION_KEY ": "
       << ToolsVersion << "\n";
   out << "// " SWIFT_MODULE_FLAGS_KEY ": "
       << Opts.ParseableInterfaceFlags << "\n";

test/ParseableInterface/Conformances.swiftinterface

@@ -1,4 +1,4 @@
-// swift-tools-version: 4.0
+// swift-compiler-version: Swift 4.0
 // swift-module-flags: 
 
 // RUN: %empty-directory(%t)

test/ParseableInterface/DefaultArgs.swiftinterface

@@ -1,4 +1,4 @@
-// swift-tools-version: 4.0
+// swift-compiler-version: Swift 4.0
 // swift-module-flags: 
 
 // RUN: %target-swift-frontend -emit-silgen %s | %FileCheck %s