Fix issue where vsproj=yes vsproj_gen_only=no sometimes fails to build

Assigning `env["CCFLAGS"]` directly to a variable causes any changes to that
variable to also be done to the original env object. This means CCFLAGS would
be modified during generation of the VS project with additional flags and
other options set by platforms.

This would normally not be noticed when just generating the project, but when
generating and building at the same time with a compiler that doesn't support
VS-style flags, this flag leakage can cause unexpected build failures.

methods.py

@@ -1274,7 +1274,7 @@ def generate_vs_project(env, original_args, project_name="godot"):
 
         props_template = props_template.replace("%%OUTPUT%%", output)
 
-        proplist = [format_key_value(v) for v in list(env["CPPDEFINES"])]
+        proplist = [format_key_value(j) for j in list(env["CPPDEFINES"])]
         proplist += [format_key_value(j) for j in env.get("VSHINT_DEFINES", [])]
         props_template = props_template.replace("%%DEFINES%%", ";".join(proplist))
 
@@ -1283,9 +1283,9 @@ def generate_vs_project(env, original_args, project_name="godot"):
         proplist += [str(j) for j in get_default_include_paths(env)]
         props_template = props_template.replace("%%INCLUDES%%", ";".join(proplist))
 
-        proplist = env["CCFLAGS"]
-        proplist += [x for x in env["CXXFLAGS"] if not x.startswith("$")]
-        proplist += [str(j) for j in env.get("VSHINT_OPTIONS", [])]
+        proplist = [env.subst("$CCFLAGS")]
+        proplist += [env.subst("$CXXFLAGS")]
+        proplist += [env.subst("$VSHINT_OPTIONS")]
         props_template = props_template.replace("%%OPTIONS%%", " ".join(proplist))
 
         # Windows allows us to have spaces in paths, so we need