bin/spec: support "special flags"

src/spec/index.ts

@@ -69,6 +69,7 @@ export interface ConfigOptions {
         CC: string,
         FC: string,
     };
+    specialFlags: string,
 }
 
 // Pure function to render configuration
@@ -81,6 +82,7 @@ export const renderConfig = (options: ConfigOptions): string => {
             .replace("@@CompilerCXX@@", options.compilerPaths.CXX)
             .replace("@@CompilerFC@@", options.compilerPaths.FC)
             .replace("@@LIBS@@", options.libs.join(" "))
+            .replace("@@SpecialFlags@@", options.specialFlags)
         ;
 };