maint: turn on gcc logical-op checking

This would have detected the bug in commit 38ad33931 (Aug 09), which
we missed until commit f828ca35 (Jul 10); over 11 months later.

However, on Fedora 13, it also triggers LOTS of warnings from
the libcurl-devel header for two files:

esx/esx_vi.c: In function 'esxVI_CURL_Perform':
esx/esx_vi.c:232: error: logical '&&' with non-zero constant will always evaluate as true [-Wlogical-op]
esx/esx_vi.c:232: error: logical '&&' with non-zero constant will always evaluate as true [-Wlogical-op]
esx/esx_vi.c:232: error: logical '&&' with non-zero constant will always evaluate as true [-Wlogical-op]
...
xenapi/xenapi_driver.c: In function 'call_func':
xenapi/xenapi_driver.c:1872: error: logical '&&' with non-zero constant will always evaluate as true [-Wlogical-op]
xenapi/xenapi_driver.c:1872: error: logical '&&' with non-zero constant will always evaluate as true [-Wlogical-op]
xenapi/xenapi_driver.c:1872: error: logical '&&' with non-zero constant will always evaluate as true [-Wlogical-op]
...

libcurl allows to disable the type-checking code that triggers those
warnings, along with the reduction in type-safety of calls to some
libcurl functions. I figure this is worth the improved compiler
checking throughout the rest of libvirt.

* acinclude.m4 (--enable-compile-warnings=error): Add -Wlogical-op.
* configure.ac: Add -DCURL_DISABLE_TYPECHECK to LIBCURL_CFLAGS to
avoid compilation warning.

Suggested by Daniel P. Berrange.
Tweaked by Matthias Bolte.

acinclude.m4

@@ -36,9 +36,19 @@ AC_DEFUN([LIBVIRT_COMPILE_WARNINGS],[
 	try_compiler_flags="-Wall -Wformat -Wformat-security -Wmissing-prototypes $common_flags"
 	;;
     maximum|error)
-	try_compiler_flags="-Wall -Wformat -Wformat-security -Wmissing-prototypes -Wnested-externs -Wpointer-arith"
-	try_compiler_flags="$try_compiler_flags -Wextra -Wshadow -Wcast-align -Wwrite-strings -Waggregate-return"
-	try_compiler_flags="$try_compiler_flags -Wstrict-prototypes -Winline -Wredundant-decls -Wno-sign-compare"
+	try_compiler_flags="-Wall -Wformat -Wformat-security"
+	try_compiler_flags="$try_compiler_flags -Wmissing-prototypes"
+	try_compiler_flags="$try_compiler_flags -Wnested-externs "
+	try_compiler_flags="$try_compiler_flags -Wpointer-arith"
+	try_compiler_flags="$try_compiler_flags -Wextra -Wshadow"
+	try_compiler_flags="$try_compiler_flags -Wcast-align"
+	try_compiler_flags="$try_compiler_flags -Wwrite-strings"
+	try_compiler_flags="$try_compiler_flags -Waggregate-return"
+	try_compiler_flags="$try_compiler_flags -Wstrict-prototypes"
+	try_compiler_flags="$try_compiler_flags -Winline"
+	try_compiler_flags="$try_compiler_flags -Wredundant-decls"
+	try_compiler_flags="$try_compiler_flags -Wno-sign-compare"
+	try_compiler_flags="$try_compiler_flags -Wlogical-op"
 	try_compiler_flags="$try_compiler_flags $common_flags"
 	if test "$enable_compile_warnings" = "error" ; then
 	    try_compiler_flags="$try_compiler_flags -Werror"

configure.ac

@@ -1631,6 +1631,12 @@ if test "$with_xenapi" = "yes" ; then
 fi
 AM_CONDITIONAL([WITH_XENAPI], [test "$with_xenapi" = "yes"])
 
+# XXX as of libcurl-devel-7.20.1-3.fc13.x86_64, curl ships a version
+# of <curl/curl.h> that #defines several wrapper macros around underlying
+# functions to add type safety for gcc only.  However, these macros
+# spuriously trip gcc's -Wlogical-op warning.  Avoid the warning by
+# disabling the wrappers; even if it removes some type-check safety.
+LIBCURL_CFLAGS="-DCURL_DISABLE_TYPECHECK $LIBCURL_CFLAGS"
 
 AC_SUBST([LIBCURL_CFLAGS])
 AC_SUBST([LIBCURL_LIBS])