Rebuild only if proto changed.

jps-plugin/testData/incremental/topLevelFunctionSameSignature/build.log

@@ -0,0 +1,7 @@
+Cleaning output files:
+out/production/module/test/TestPackage-fun-*.class
+out/production/module/test/TestPackage.class
+End of files
+Compiling files:
+src/fun.kt
+End of files

jps-plugin/testData/incremental/topLevelFunctionSameSignature/fun.kt

@@ -0,0 +1,4 @@
+package test
+
+fun foo() {
+}

jps-plugin/testData/incremental/topLevelFunctionSameSignature/fun.kt.new

@@ -0,0 +1,5 @@
+package test
+
+fun foo() {
+    println("body is changed, but it doesn't matter, we won't rebuild dependencies")
+}

jps-plugin/testData/incremental/topLevelFunctionSameSignature/usage.kt

@@ -0,0 +1,5 @@
+package test
+
+fun usage() {
+    foo()
+}