[lldb][test] Set target OS for API tests in case of remote testing

Makefile.rules uses HOST_OS and OS variables for determining host and target
OSes for API tests compilation.

When lldb's target is set to remote-linux, Makefile.rules script should be
executed with the target OS variable set to Linux.

This is useful for the case of Windows-to-Linux cross-testing.

Author: dzhidzhoev

lldb/packages/Python/lldbsuite/test/lldbplatformutil.py

@@ -56,6 +56,10 @@ def target_is_android():
     return configuration.lldb_platform_name == "remote-android"
 
 
+def target_is_remote_linux():
+    return configuration.lldb_platform_name == "remote-linux"
+
+
 def android_device_api():
     if not hasattr(android_device_api, "result"):
         assert configuration.lldb_platform_url is not None
@@ -97,6 +101,9 @@ def finalize_build_dictionary(dictionary):
             dictionary = {}
         dictionary["OS"] = "Android"
         dictionary["PIE"] = 1
+    elif target_is_remote_linux():
+        dictionary = dictionary or {}
+        dictionary["OS"] = "Linux"
     return dictionary