Compiler Gradle options

There are several gradle flags one can use for Konan build.

-Pbuild_flags passes flags to the compiler used to build stdlib

  ./gradlew -Pbuild_flags="--disable lower_inline --print_ir" stdlib

-Pshims compiles LLVM interface with tracing "shims". Allowing one to trace the LLVM calls from the compiler. Make sure to rebuild the project.
```
  ./gradlew -Pshims=true dist
```

-Pfilter allows one to choose test files to run.

  ./gradlew -Pfilter=overflowLong.kt run_external

-Pprefix allows one to choose external test directories to run. Only tests from directories with given prefix will be executed.
```
  ./gradlew -Pprefix=external_codegen_box_cast run_external
```

Testing

To run blackbox compiler tests from JVM Kotlin use (takes time):

./gradlew run_external

To update the blackbox compiler tests set TeamCity build number in gradle.properties:

testDataVersion=<build number>:id

and run ./gradlew update_external_tests

-Ptest_flags passes flags to the compiler used to compile tests

  ./gradlew -Ptest_flags="--time" backend.native:tests:array0

-Ptest_target specifies cross target for a test run.

  ./gradlew -Ptest_target=raspberrypi backend.native:tests:array0

-Premote=user@host sets remote test execution login/hostname. Good for cross compiled tests.
```
  ./gradles -Premote=kotlin@111.22.33.444 backend.native:tests:run
```