manual c function interop

LANGUAGE.md

@@ -21,6 +21,8 @@
 
 - demand-monomorphized functions
 - bodyful `c func` definitions using the c calling convention
+- bodyless `c func` declarations with exact, globally unique external symbol names
+- concrete-only foreign signatures
 - directory packages with merged declarations
 - file-local relative imports, aliases, and qualified member access
 
@@ -28,15 +30,14 @@
 
 - error-tolerant compilation with runtime diagnostic traps
 - lazy semantic checking of demanded function specializations
+- demand-driven LLVM declarations for referenced foreign functions
+- ordered linking of additional c sources, objects, and libraries
 - static, eager runtime, and deferred problematic globals
 
 ## PLANNED
 
 ### foreign functions and linking
 
-- bodyless `c func` declarations with exact external symbol names
-- concrete-only foreign signatures
-- linking c sources, objects, and libraries
 - c variadic calls with default argument promotions
 - exporting brolang functions to c