ImmutableBinaryBlob.asCPointer: fix + test (#1879)

backend.native/tests/build.gradle

@@ -2734,6 +2734,12 @@ task interop4(type: RunInteropKonanTest) {
     interop = 'cstdio'
 }
 
+task interop5(type: RunStandaloneKonanTest) {
+    disabled = (project.testTarget == 'wasm32') // No interop for wasm yet.
+    goldValue = "Hello!\n"
+    source = "interop/basics/5.kt"
+}
+
 task interop_bitfields(type: RunInteropKonanTest) {
     disabled = (project.testTarget == 'wasm32') // No interop for wasm yet.
     expectedFail = (project.testTarget == 'linux_mips32') // fails because of big-endiannes

backend.native/tests/interop/basics/5.kt

@@ -0,0 +1,7 @@
+import platform.posix.printf
+
+val golden = immutableBinaryBlobOf(0x48, 0x65, 0x6C, 0x6C, 0x6F, 0x21, 0x00).asCPointer(0)
+
+fun main(args: Array<String>) {
+    printf("%s\n", golden)
+}