Printing linker error message from gradle MPP plugin (#3979)

backend.native/compiler/ir/backend.native/src/org/jetbrains/kotlin/backend/konan/Linker.kt

@@ -133,7 +133,7 @@ internal class Linker(val context: Context) {
                 it.execute()
             }
         } catch (e: KonanExternalToolFailure) {
-            context.reportCompilationError("${e.toolName} invocation reported errors")
+            context.reportCompilationError("${e.toolName} invocation reported errors\n${e.message}")
         }
         return executable
     }

shared/src/main/kotlin/org/jetbrains/kotlin/konan/exec/ExecuteCommand.kt

@@ -16,9 +16,10 @@
 
 package org.jetbrains.kotlin.konan.exec
 
-import java.lang.ProcessBuilder
-import java.lang.ProcessBuilder.Redirect
 import org.jetbrains.kotlin.konan.KonanExternalToolFailure
+import java.io.BufferedReader
+import java.io.InputStreamReader
+import java.lang.ProcessBuilder.Redirect
 
 
 open class Command(initialCommand: List<String>) {
@@ -42,28 +43,33 @@ open class Command(initialCommand: List<String>) {
 
     var logger: ((() -> String)->Unit)? = null
 
+    private var stdError: List<String> = emptyList()
+
     fun logWith(newLogger: ((() -> String)->Unit)): Command {
         logger = newLogger
         return this
     }
 
     open fun runProcess(): Int {
+        stdError = emptyList()
         val builder = ProcessBuilder(command)
 
         builder.redirectOutput(Redirect.INHERIT)
         builder.redirectInput(Redirect.INHERIT)
-        builder.redirectError(Redirect.INHERIT)
 
         val process = builder.start()
+
+        val reader = BufferedReader(InputStreamReader(process.errorStream))
+        stdError = reader.readLines()
+
         val exitCode = process.waitFor()
         return exitCode
     }
 
     open fun execute() {
         log()
-
         val code = runProcess()
-        handleExitCode(code)
+        handleExitCode(code, stdError)
     }
 
     /**
@@ -104,8 +110,15 @@ open class Command(initialCommand: List<String>) {
     private fun handleExitCode(code: Int, output: List<String> = emptyList()) {
         if (code != 0) throw KonanExternalToolFailure("""
             The ${command[0]} command returned non-zero exit code: $code.
-            output: ${output.joinToString("\n")}
+            output:
+            ${output.joinToString("\n")}
             """.trimIndent(), command[0])
+        // Show warnings in case of success linkage.
+        if (stdError.isNotEmpty()) {
+            stdError.joinToString("\n").also { message ->
+                logger?.let { it { message } } ?: println(message)
+            }
+        }
     }
 
     private fun log() {