parseFnDecl parses the optional [LIB] ["csym"] tail after the
extern/export keyword into FnDecl.extern_lib/extern_name (mirrors
'#foreign LIB "csym"'). declareFunction unifies the symbol-name
override: rename_c_name = foreign_expr.c_name (for #foreign) OR
fd.extern_name (for extern) -> declare under the C name and map sx->C
in foreign_name_map; the dedupe guard now covers extern too.
examples/1224 green: 'c_abs :: (n) -> i32 extern "abs";' resolves
c_abs to libc abs -> c_abs(-42) = 42. 1223 (bare extern) unregressed.
Suite green (635 corpus / 443 unit).
extern_lib is parsed + stored but not a linking driver — like
'#foreign libc', it references a lib; the #library decl + build flags
remain the separate linking axis (decision 4). green commit.
5777ff62ad