Automatically add cross-mingw root and sysroot bindir to WINEPATH

This ensures that all the system DLLs required by executables such as
libstdc++-6.dll can be found out of the box and tests can run

mesonbuild/backend/backends.py

@@ -567,28 +567,41 @@ class Backend:
             args.append(d_arg)
         return args
 
-    def determine_windows_extra_paths(self, target, extra_bdeps):
+    def get_mingw_extra_paths(self):
+        paths = []
+        # The cross bindir
+        root = self.environment.cross_info.get_root()
+        if root:
+            paths.append(os.path.join(root, 'bin'))
+        # The toolchain bindir
+        sys_root = self.environment.cross_info.get_sys_root()
+        if sys_root:
+            paths.append(os.path.join(sys_root, 'bin'))
+        return paths
+
+    def determine_windows_extra_paths(self, target, extra_bdeps, is_cross=False):
         '''On Windows there is no such thing as an rpath.
         We must determine all locations of DLLs that this exe
         links to and return them so they can be used in unit
         tests.'''
-        result = []
-        prospectives = []
+        result = set()
+        prospectives = set()
         if isinstance(target, build.BuildTarget):
-            prospectives = target.get_transitive_link_deps()
+            prospectives.update(target.get_transitive_link_deps())
             # External deps
             for deppath in self.rpaths_for_bundled_shared_libraries(target):
-                result.append(os.path.normpath(os.path.join(self.environment.get_build_dir(), deppath)))
+                result.add(os.path.normpath(os.path.join(self.environment.get_build_dir(), deppath)))
         for bdep in extra_bdeps:
-            prospectives += bdep.get_transitive_link_deps()
+            prospectives.update(bdep.get_transitive_link_deps())
         # Internal deps
         for ld in prospectives:
             if ld == '' or ld == '.':
                 continue
             dirseg = os.path.join(self.environment.get_build_dir(), self.get_target_dir(ld))
-            if dirseg not in result:
-                result.append(dirseg)
-        return result
+            result.add(dirseg)
+        if is_cross:
+            result.update(self.get_mingw_extra_paths())
+        return list(result)
 
     def write_benchmark_file(self, datafile):
         self.write_test_serialisation(self.build.get_benchmarks(), datafile)
@@ -622,7 +635,7 @@ class Backend:
                 extra_bdeps = []
                 if isinstance(exe, build.CustomTarget):
                     extra_bdeps = exe.get_transitive_build_target_deps()
-                extra_paths = self.determine_windows_extra_paths(exe, extra_bdeps)
+                extra_paths = self.determine_windows_extra_paths(exe, extra_bdeps, is_cross)
             else:
                 extra_paths = []
             cmd_args = []

mesonbuild/backend/ninjabackend.py

@@ -536,7 +536,8 @@ int dummy;
         if mesonlib.for_windows(is_cross, self.environment) or \
            mesonlib.for_cygwin(is_cross, self.environment):
             extra_bdeps = target.get_transitive_build_target_deps()
-            extra_paths = self.determine_windows_extra_paths(target.command[0], extra_bdeps)
+            extra_paths = self.determine_windows_extra_paths(target.command[0],
+                                                             extra_bdeps, is_cross)
             if extra_paths:
                 serialize = True
         if serialize:

mesonbuild/environment.py

@@ -1045,6 +1045,12 @@ class CrossBuildInfo:
     def get_properties(self):
         return self.config['properties']
 
+    def get_root(self):
+        return self.get_properties().get('root', None)
+
+    def get_sys_root(self):
+        return self.get_properties().get('sys_root', None)
+
     # When compiling a cross compiler we use the native compiler for everything.
     # But not when cross compiling a cross compiler.
     def need_cross_compiler(self):