build: use -fparse-all-comments with -Wdocumentation

Clang checks only /** ... */ comments without this flag.

* configure.ac (warn_common): Also check -fparse-all-comments.

configure.ac

@@ -84,7 +84,8 @@ AC_ARG_ENABLE([gcc-warnings],
               [enable_gcc_warnings=no])
 AM_CONDITIONAL([ENABLE_GCC_WARNINGS], [test "$enable_gcc_warnings" = yes])
 if test "$enable_gcc_warnings" = yes; then
-  warn_common='-Wall -Wextra -Wno-sign-compare -Wcast-align -Wdocumentation
+  warn_common='-Wall -Wextra -Wno-sign-compare -Wcast-align
+    -fparse-all-comments -Wdocumentation
     -Wformat -Wnull-dereference -Wpointer-arith -Wwrite-strings'
   warn_c='-Wbad-function-cast -Wshadow -Wstrict-prototypes'
   warn_cxx='-Wnoexcept'

data/lalr1.cc

@@ -344,7 +344,7 @@ b4_location_define])])[
     ///             if null, no trace is output.
     /// \param s    the state
     /// \param sym  the symbol (for its value and location).
-    /// \warning the contents of \a s.value is stolen.
+    /// \warning the contents of \a sym.value is stolen.
     void yypush_ (const char* m, state_type s, symbol_type& sym);
 
     /// Pop \a n symbols the three stacks.