meson: create unique names for build directory (#32062)

Taken from CMakePackage

lib/spack/spack/build_systems/meson.py

@@ -138,13 +138,21 @@ def flags_to_build_system_args(self, flags):
         # Has to be dynamic attribute due to caching
         setattr(self, "meson_flag_args", [])
 
+    @property
+    def build_dirname(self):
+        """Returns the directory name to use when building the package
+
+        :return: name of the subdirectory for building the package
+        """
+        return "spack-build-%s" % self.spec.dag_hash(7)
+
     @property
     def build_directory(self):
         """Returns the directory to use when building the package
 
         :return: directory where to build the package
         """
-        return os.path.join(self.stage.source_path, "spack-build")
+        return os.path.join(self.stage.path, self.build_dirname)
 
     def meson_args(self):
         """Produces a list containing all the arguments that must be passed to