AC_CHECK_DECL, AC_CHECK_DECLS: port to the Clang compiler

* lib/autoconf/general.m4 (_AC_UNDECLARED_WARNING): New macro.
(_AC_CHECK_DECL_BODY): Call it once per language; treat warnings as
errors when its verdict indicates that.
* tests/semantics.at (AC_CHECK_DECLS): Add a macro call that relies on
the new semantics.  Avoid -Wmissing-variable-declarations warnings.
* doc/autoconf.texi (Generic Declarations): Document the implications.
* NEWS: Mention this change.

1 files changed, 12 insertions, 0 deletions

diff --git a/doc/autoconf.texi b/doc/autoconf.texi
index b2ca0ae5..8c4302d3 100644
--- a/doc/autoconf.texi
+++ b/doc/autoconf.texi
@@ -6315,6 +6315,12 @@ parentheses for types which can be zero-initialized:
 AC_CHECK_DECL([basename(char *)])
 @end example
 
+Some compilers don't indicate every missing declaration by the error
+status.  This macro checks the standard error from such compilers and
+considers a declaration missing if any warnings have been reported.  For
+most compilers, though, warnings do not affect this macro's outcome
+unless @code{AC_LANG_WERROR} is also specified.
+
 This macro caches its result in the @code{ac_cv_have_decl_@var{symbol}}
 variable, with characters not suitable for a variable name mapped to
 underscores.
@@ -6375,6 +6381,12 @@ You fall into the second category only in extreme situations: either
 your files may be used without being configured, or they are used during
 the configuration.  In most cases the traditional approach is enough.
 
+Some compilers don't indicate every missing declaration by the error
+status.  This macro checks the standard error from such compilers and
+considers a declaration missing if any warnings have been reported.  For
+most compilers, though, warnings do not affect this macro's outcome
+unless @code{AC_LANG_WERROR} is also specified.
+
 This macro caches its results in @code{ac_cv_have_decl_@var{symbol}}
 variables, with characters not suitable for a variable name mapped to
 underscores.