[lldb][test] Set target and host 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.

This commit starts moving the platform detection logic from Makefile to Python lldb
test suite.

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
@@ -92,11 +96,22 @@ def match_android_device(device_arch, valid_archs=None, valid_api_levels=None):
 
 
 def finalize_build_dictionary(dictionary):
+    if dictionary is None:
+        dictionary = {}
     if target_is_android():
-        if dictionary is None:
-            dictionary = {}
         dictionary["OS"] = "Android"
         dictionary["PIE"] = 1
+    elif platformIsDarwin():
+        dictionary["OS"] = "Darwin"
+    else:
+        # Provide uname-like platform name
+        platform_name_to_uname = { "linux": "Linux",
+                "netbsd": "NetBSD",
+                "freebsd": "FreeBSD",
+                "windows": "Windows_NT",
+                }
+        dictionary["OS"] = platform_name_to_uname[getPlatform()]
+        dictionary["HOST_OS"] = platform_name_to_uname[getHostPlatform()]
     return dictionary