Get rid of old boilerplate in configure.ac, and enforce -Wextra -std=c99

configure.ac

 AC_PREREQ(2.59)
 AC_COPYRIGHT([Copyright (c) 2015 UPLEX Nils Goroll Systemoptimierung])
-AC_INIT([libvmod-backend_dyn], [trunk])
+AC_INIT([VMOD backend_dyn], [trunk], [varnish-support@uplex.de],
+        [libvmod-backend_dyn],
+	[https://code.uplex.de/uplex-varnish/libvmod-gcrypt])
 AC_CONFIG_MACRO_DIR([m4])
-m4_ifndef([VARNISH_VMOD_INCLUDES], AC_MSG_ERROR([Need varnish.m4 -- see README.rst]))
+m4_ifndef([VARNISH_VMOD_INCLUDES],
+          AC_MSG_ERROR([Need varnish.m4 -- see INSTALL.rst]))
 AC_CONFIG_SRCDIR(src/vmod.vcc)
 AM_CONFIG_HEADER(config.h)
 
@@ -74,60 +77,6 @@ AC_PATH_PROG([VARNISHTEST], [varnishtest], [],
 AC_PATH_PROG([VARNISHD], [varnishd], [],
     [$LIBVARNISHAPI_SBINDIR:$LIBVARNISHAPI_BINDIR:$PATH])
 
-##
-## --enable-developer-warnings, --enable-stack-protector and
-## --enable-debugging-symbols from Varnish 4.1 configure.ac
-##
-
-#######################################################################
-# Now that we're done using the compiler to look for functions and
-# libraries, set CFLAGS to what we want them to be for our own code
-
-# This is a test to see how much havoc Jenkins exposes.
-#
-# The reason for -Wno-error=unused-result is a glibc/gcc interaction
-# idiocy where write is marked as warn_unused_result, causing build
-# failures.
-CFLAGS="${CFLAGS} -Wall -Werror"
-OCFLAGS="${OCFLAGS} -Wall -Werror"
-AX_CHECK_COMPILE_FLAG([-Werror=unused-result],
-    [CFLAGS="${CFLAGS} -Wno-error=unused-result"
-     OCFLAGS="${OCFLAGS} -Wno-error=unused-result"],
-    [AX_CHECK_COMPILE_FLAG([-Wunused-result],
-     [CFLAGS="${CFLAGS} -Wno-unused-result"
-      OCFLAGS="${OCFLAGS} -Wno-unused-result"])])
-
-# This corresponds to FreeBSD's WARNS level 6
-DEVELOPER_CFLAGS=" \
-	-Werror \
-	-Wall \
-	-Wno-format-y2k \
-	-W \
-	-Wstrict-prototypes \
-	-Wmissing-prototypes \
-	-Wpointer-arith \
-	-Wreturn-type \
-	-Wcast-qual \
-	-Wwrite-strings \
-	-Wswitch \
-	-Wshadow \
-	-Wunused-parameter \
-	-Wcast-align \
-	-Wchar-subscripts \
-	-Wnested-externs \
-	-Wextra \
-	-Wno-sign-compare \
-"
-
-# These are not compliable yet
-DEVELOPER_GCC_CFLAGS="-Wold-style-definition -Wredundant-decls "
-#DEVELOPER_CFLAGS="${DEVELOPER_CFLAGS} ${DEVELOPER_GCC_CFLAGS}"
-
-# These are compilable
-DEVELOPER_CLANG_CFLAGS="-Wmissing-variable-declarations -Wno-string-plus-int"
-# -Wno-empty-body
-#DEVELOPER_CFLAGS="${DEVELOPER_CFLAGS} ${DEVELOPER_CLANG_CFLAGS}"
-
 # --enable-stack-protector
 AC_ARG_ENABLE(stack-protector,
        AS_HELP_STRING([--enable-stack-protector],[enable stack protector (default is YES)]),
@@ -141,36 +90,24 @@ if test "x$enable_stack_protector" != "xno"; then
 		[], [])
 fi
 
-# --enable-developer-warnings
-AC_ARG_ENABLE(developer-warnings,
-	AS_HELP_STRING([--enable-developer-warnings],[enable strict warnings (default is NO)]),
+# --enable-debugging
+AC_ARG_ENABLE(debugging,
+	AS_HELP_STRING([--enable-debugging],[enable debugging (default is NO)]),
 	[],
-	[enable_developer_warnings=no])
-
-if test "x$enable_developer_warnings" != "xno"; then
-	# compiler flags not available on gcc3
-	AX_CHECK_COMPILE_FLAG([-Wno-pointer-sign],
-		[DEVELOPER_CFLAGS="${DEVELOPER_CFLAGS} -Wno-pointer-sign"], [], [])
-	# Not available in gcc 4.1.2
-	AX_CHECK_COMPILE_FLAG([-Wno-address],
-		[DEVELOPER_CFLAGS="${DEVELOPER_CFLAGS} -Wno-address"])
-
-	# no known way to specifically disabling missing-field-initializers warnings
-	# keeping the rest of Wextra
-	AX_CHECK_COMPILE_FLAG([-Wno-missing-field-initializers],
-		[DEVELOPER_CFLAGS="${DEVELOPER_CFLAGS} -Wno-missing-field-initializers"],
-		[DEVELOPER_CFLAGS="${DEVELOPER_CFLAGS} -Wno-extra"],
+	[enable_debugging=no])
+
+# AC_PROG_CC sets CFLAGS to '-g -O2' unless it is already set, so
+# there's no need to add -g. Disable or change by explicitly setting
+# CFLAGS. If this option is enabled, then -Og or -O0 becomes the last
+# optimization option, and hence takes precedence.
+if test "x$enable_debugging" != "xno"; then
+	CFLAGS="${CFLAGS} -fno-inline"
+	AX_CHECK_COMPILE_FLAG([-Og],
+		[CFLAGS="${CFLAGS} -Og"],
+		[CFLAGS="${CFLAGS} -O0"],
 		[])
-
-	CFLAGS="${CFLAGS} ${DEVELOPER_CFLAGS}"
-	OCFLAGS="${OCFLAGS} ${DEVELOPER_CFLAGS}"
 fi
 
-# --enable-debugging-symbols
-AC_ARG_ENABLE(debugging-symbols,
-	AS_HELP_STRING([--enable-debugging-symbols],[enable debugging symbols (default is NO)]),
-	CFLAGS="${CFLAGS} -O0 -g -fno-inline")
-
 AC_CONFIG_FILES([
 	Makefile
 	src/Makefile

src/Makefile.am

-AM_CPPFLAGS = @VMOD_INCLUDES@ -Wall -Werror
+AM_CPPFLAGS = @VMOD_INCLUDES@ -Wall -Werror -Wextra -std=c99
 
 vmoddir = @VMOD_DIR@
 vmod_LTLIBRARIES = libvmod_backend_dyn.la