Enable various compiler warnings

Signed-off-by: David Woodhouse <David.Woodhouse@intel.com>

acinclude.m4

@@ -0,0 +1,61 @@
+dnl as-compiler-flag.m4 0.1.0
+
+dnl autostars m4 macro for detection of compiler flags
+
+dnl David Schleef <ds@schleef.org>
+
+dnl $Id: as-compiler-flag.m4,v 1.1 2005/12/15 23:35:19 ds Exp $
+
+dnl AS_COMPILER_FLAG(CFLAGS, ACTION-IF-ACCEPTED, [ACTION-IF-NOT-ACCEPTED])
+dnl Tries to compile with the given CFLAGS.
+dnl Runs ACTION-IF-ACCEPTED if the compiler can compile with the flags,
+dnl and ACTION-IF-NOT-ACCEPTED otherwise.
+
+AC_DEFUN([AS_COMPILER_FLAG],
+[
+  AC_MSG_CHECKING([to see if compiler understands $1])
+
+  save_CFLAGS="$CFLAGS"
+  CFLAGS="$CFLAGS $1"
+
+  AC_TRY_COMPILE([ ], [], [flag_ok=yes], [flag_ok=no])
+  CFLAGS="$save_CFLAGS"
+
+  if test "X$flag_ok" = Xyes ; then
+    m4_ifvaln([$2],[$2])
+    true
+  else
+    m4_ifvaln([$3],[$3])
+    true
+  fi
+  AC_MSG_RESULT([$flag_ok])
+])
+
+dnl AS_COMPILER_FLAGS(VAR, FLAGS)
+dnl Tries to compile with the given CFLAGS.
+
+AC_DEFUN([AS_COMPILER_FLAGS],
+[
+  list=$2
+  flags_supported=""
+  flags_unsupported=""
+  AC_MSG_CHECKING([for supported compiler flags])
+  for each in $list
+  do
+    save_CFLAGS="$CFLAGS"
+    CFLAGS="$CFLAGS $each"
+    AC_TRY_COMPILE([ ], [], [flag_ok=yes], [flag_ok=no])
+    CFLAGS="$save_CFLAGS"
+
+    if test "X$flag_ok" = Xyes ; then
+      flags_supported="$flags_supported $each"
+    else
+      flags_unsupported="$flags_unsupported $each"
+    fi
+  done
+  AC_MSG_RESULT([$flags_supported])
+  if test "X$flags_unsupported" != X ; then
+    AC_MSG_WARN([unsupported compiler flags: $flags_unsupported])
+  fi
+  $1="$$1 $flags_supported"
+])

configure.ac

@@ -5,6 +5,26 @@ AC_LANG_C
 AM_INIT_AUTOMAKE([foreign])
 m4_ifdef([AM_SILENT_RULES], [AM_SILENT_RULES([yes])])
 
+AS_COMPILER_FLAGS(CFLAGS,
+        "-Wall
+         -Wextra
+         -Wno-missing-field-initializers
+         -Wno-sign-compare
+         -Wno-unused-parameter
+         -Werror=pointer-to-int-cast
+         -Wdeclaration-after-statement
+         -Werror-implicit-function-declaration
+         -Wformat-nonliteral
+         -Wformat-security
+         -Winit-self
+         -Wmissing-declarations
+         -Wmissing-include-dirs
+         -Wmissing-noreturn
+         -Wnested-externs
+         -Wpointer-arith
+         -Wundef
+         -Wwrite-strings")
+
 AC_ARG_WITH([openssl],
             AS_HELP_STRING([--with-openssl],
                            [Location of OpenSSL build dir]),