runtime/build.gradle: extract bitcode compilation to custom task class

runtime/build.gradle

@@ -1,39 +1,12 @@
+import org.jetbrains.kotlin.CompileCppToBitcode
+
 // TODO: consider using some Gradle plugins to build and test
 
-def srcDir = 'src/main/cpp'
-def objDir = "$buildDir/bitcode"
-def outFile = "$buildDir/runtime.bc"
 
-task compile(type: Exec) {
-    doFirst {
-         new File(objDir).mkdirs()
-    }
+task build(type: CompileCppToBitcode) {
+    name 'runtime'
+    srcRoot file('src/main')
 
-    inputs.dir srcDir
-    outputs.dir objDir
-
-    workingDir objDir
-
-    executable "$llvmInstallPath/bin/clang"
-    args '-std=c++11'
-
-    args '-c', '-emit-llvm'
-
-    args fileTree(srcDir).include('**/*.cpp')
-}
-
-task build(type: Exec) {
-    dependsOn compile
-
-    inputs.dir objDir
-    outputs.file outFile
-
-    executable "$llvmInstallPath/bin/llvm-link"
-    args '-o', outFile
-
-    doFirst {
-        args fileTree(objDir).include('**/*.bc')
-    }
 }
 
 task test {
@@ -44,7 +17,7 @@ task test {
 	    commandLine "$llvmInstallPath/bin/clang", 'src/test/c/main.c', '-c', '-emit-llvm', '-o', "$buildDir/main.bc"
 	}
         exec {
-	    commandLine "$llvmInstallPath/bin/clang++", outFile, "$buildDir/main.bc", '-o', "$buildDir/main"
+	    commandLine "$llvmInstallPath/bin/clang++", build.outFile, "$buildDir/main.bc", '-o', "$buildDir/main"
 	}
 	exec {
 	    workingDir buildDir