[LLDB][test] Update Makefile.rules to support Windows host+Linux target

These changes are aimed to support cross compilation build on Windows
host for Linux target for API tests execution. They're not final:
changes will follow for refactoring and adjustments to make all tests
passing.

Chocolatey make is recommended to use, since it is maintained
better than GnuWin32 recommended here https://lldb.llvm.org/resources/build.html#codesigning
(it was updated last time in 2010) and helps to avoid problems
with building tests (for example, GnuWin32 doesn't support long paths
and there are some other failures with building for Linux with it).

Author: dzhidzhoev

lldb/packages/Python/lldbsuite/test/make/Makefile.rules

@@ -112,14 +112,26 @@ $(error "C compiler is not specified. Please run tests through lldb-dotest or li
 endif
 
 #----------------------------------------------------------------------
-# Handle SDKROOT on Darwin
+# Handle SDKROOT for the cross platform builds.
 #----------------------------------------------------------------------
 
 ifeq "$(OS)" "Darwin"
     ifeq "$(SDKROOT)" ""
 	# We haven't otherwise set the SDKROOT, so set it now to macosx
 	SDKROOT := $(shell xcrun --sdk macosx --show-sdk-path)
     endif
+    SYSROOT_FLAGS := -isysroot "$(SDKROOT)"
+    GCC_TOOLCHAIN_FLAGS :=
+else
+    ifneq "$(SDKROOT)" ""
+        SYSROOT_FLAGS := --sysroot "$(SDKROOT)"
+        GCC_TOOLCHAIN_FLAGS := --gcc-toolchain="$(SDKROOT)/usr"
+    else
+        # Do not set up these options if SDKROOT was not specified.
+        # This is a regular build in that case (or Android).
+        SYSROOT_FLAGS :=
+        GCC_TOOLCHAIN_FLAGS :=
+    endif
 endif
 
 #----------------------------------------------------------------------
@@ -210,20 +222,15 @@ endif
 DEBUG_INFO_FLAG ?= -g
 
 CFLAGS ?= $(DEBUG_INFO_FLAG) -O0
-
-ifeq "$(OS)" "Darwin"
-	ifneq "$(SDKROOT)" ""
-		CFLAGS += -isysroot "$(SDKROOT)"
-	endif
-endif
+CFLAGS += $(SYSROOT_FLAGS)
 
 ifeq "$(OS)" "Darwin"
 	CFLAGS += $(ARCHFLAG) $(ARCH) $(FRAMEWORK_INCLUDES)
 else
 	CFLAGS += $(ARCHFLAG)$(ARCH)
 endif
-CFLAGS += -I$(LLDB_BASE_DIR)include -I$(LLDB_OBJ_ROOT)/include
 
+CFLAGS += -I$(LLDB_BASE_DIR)/include -I$(LLDB_OBJ_ROOT)/include
 CFLAGS += -I$(SRCDIR) -I$(THIS_FILE_DIR)
 
 ifndef NO_TEST_COMMON_H
@@ -234,9 +241,9 @@ CFLAGS += $(NO_LIMIT_DEBUG_INFO_FLAGS) $(ARCH_CFLAGS)
 
 # Use this one if you want to build one part of the result without debug information:
 ifeq "$(OS)" "Darwin"
-	CFLAGS_NO_DEBUG = -O0 $(ARCHFLAG) $(ARCH) $(FRAMEWORK_INCLUDES) $(ARCH_CFLAGS) $(CFLAGS_EXTRAS) -isysroot "$(SDKROOT)"
+	CFLAGS_NO_DEBUG = -O0 $(ARCHFLAG) $(ARCH) $(FRAMEWORK_INCLUDES) $(ARCH_CFLAGS) $(CFLAGS_EXTRAS) $(SYSROOT_FLAGS)
 else
-	CFLAGS_NO_DEBUG = -O0 $(ARCHFLAG)$(ARCH) $(FRAMEWORK_INCLUDES) $(ARCH_CFLAGS) $(CFLAGS_EXTRAS)
+	CFLAGS_NO_DEBUG = -O0 $(ARCHFLAG)$(ARCH) $(FRAMEWORK_INCLUDES) $(ARCH_CFLAGS) $(CFLAGS_EXTRAS) $(SYSROOT_FLAGS)
 endif
 
 ifeq "$(MAKE_DWO)" "YES"
@@ -267,7 +274,9 @@ endif
 CFLAGS += $(CFLAGS_EXTRAS)
 CXXFLAGS += -std=c++11 $(CFLAGS) $(ARCH_CXXFLAGS)
 LD = $(CC)
-LDFLAGS ?= $(CFLAGS)
+# Copy common options to the linker flags (dwarf, arch. & etc).
+# Note: we get some 'garbage' options for linker here (such as -I, --isystem & etc).
+LDFLAGS += $(CFLAGS)
 LDFLAGS += $(LD_EXTRAS) $(ARCH_LDFLAGS)
 ifeq (,$(filter $(OS), Windows_NT Android Darwin))
 	ifneq (,$(filter YES,$(ENABLE_THREADS)))
@@ -378,11 +387,28 @@ ifeq (1, $(USE_SYSTEM_STDLIB))
 	endif
 endif
 
+# No C++ library has been specifieed. Use libstdc++ by default.
+ifeq (,$(filter 1, $(USE_LIBSTDCPP) $(USE_LIBCPP) $(USE_SYSTEM_STDLIB)))
+  # If no explicit request was made, but we have paths to a custom libcxx, use
+  # them.
+  ifneq ($(and $(LIBCPP_INCLUDE_DIR), $(LIBCPP_LIBRARY_DIR)),)
+    CXXFLAGS += -nostdlib++ -nostdinc++ -cxx-isystem $(LIBCPP_INCLUDE_DIR)
+    ifneq "$(LIBCPP_INCLUDE_TARGET_DIR)" ""
+      CXXFLAGS += -cxx-isystem $(LIBCPP_INCLUDE_TARGET_DIR)
+    endif
+    LDFLAGS += -L$(LIBCPP_LIBRARY_DIR) -Wl,-rpath,$(LIBCPP_LIBRARY_DIR) -lc++
+  # Otherwise no C++ library has been specified. Use stdc++ by default.
+  else
+    USE_SYSTEM_STDLIB := 1
+  endif
+endif
+
 ifeq (1,$(USE_LIBSTDCPP))
 	# Clang requires an extra flag: -stdlib=libstdc++
 	ifneq (,$(findstring clang,$(CC)))
-		CXXFLAGS += -stdlib=libstdc++
-		LDFLAGS += -stdlib=libstdc++
+    # Force clang looking for the gcc's headers at specific rootfs folder.
+		CXXFLAGS += -stdlib=libstdc++ $(GCC_TOOLCHAIN_FLAGS)
+		LDFLAGS += -stdlib=libstdc++ $(GCC_TOOLCHAIN_FLAGS)
 	endif
 endif
 
@@ -403,7 +429,7 @@ ifeq (1,$(USE_LIBCPP))
 		endif
 		ifneq (,$(filter $(OS), FreeBSD Linux NetBSD))
 				ifneq (,$(LLVM_LIBS_DIR))
-				LDFLAGS += -Wl,-rpath,$(LLVM_LIBS_DIR)
+            LDFLAGS += -Wl,-rpath,$(LLVM_LIBS_DIR)
 				endif
 		endif
 	endif
@@ -416,21 +442,15 @@ ifeq (1, $(USE_SYSTEM_STDLIB))
         endif
         CXXFLAGS += -nostdlib++ -nostdinc++ -cxx-isystem $(SDKROOT)/usr/include/c++/v1
         LDFLAGS += -L$(SDKROOT)/usr/lib -Wl,-rpath,$(SDKROOT)/usr/lib -lc++
+    else
+        ifneq (,$(findstring clang,$(CC)))
+            # Force clang looking for the gcc's headers at specific rootfs folder.
+            CXXFLAGS += -stdlib=libstdc++ $(GCC_TOOLCHAIN_FLAGS)
+            LDFLAGS += -stdlib=libstdc++ $(GCC_TOOLCHAIN_FLAGS)
+        endif
     endif
 endif
 
-# If no explicit request was made, but we have paths to a custom libcxx, use
-# them.
-ifeq ($(or $(USE_LIBSTDCPP), $(USE_LIBCPP), $(USE_SYSTEM_STDLIB)),)
-	ifneq ($(and $(LIBCPP_INCLUDE_DIR), $(LIBCPP_LIBRARY_DIR)),)
-		CXXFLAGS += -nostdlib++ -nostdinc++ -cxx-isystem $(LIBCPP_INCLUDE_DIR)
-		ifneq "$(LIBCPP_INCLUDE_TARGET_DIR)" ""
-				CXXFLAGS += -cxx-isystem $(LIBCPP_INCLUDE_TARGET_DIR)
-		endif
-		LDFLAGS += -L$(LIBCPP_LIBRARY_DIR) -Wl,-rpath,$(LIBCPP_LIBRARY_DIR) -lc++
-	endif
-endif
-
 #----------------------------------------------------------------------
 # Additional system libraries
 #----------------------------------------------------------------------