m4: disable gcc8 -Wcast-function-type warnings from -Wextra

The -Wextra flag bundle gained a new warning -Wcast-function-type.
This complains if you cast between two function prototypes where
the number of parameters or their data types are not compatible.
Unfortunately we need such "bad" function casts for our event
callbacks. It is possible to silence the warning by first casting
to the generic "void (*)(void)" function prototype, but that is
rather ugly to add throughout libvirt code.

Signed-off-by: Daniel P. Berrangé <berrange@redhat.com>

diff --git a/m4/virt-compile-warnings.m4 b/m4/virt-compile-warnings.m4
index b9c9748420dc1b468749789cebc89e8d23636f28..4b35a6f6b5b02730b7d8bcfdfc772f03f20196e3 100644 (file)
--- a/m4/virt-compile-warnings.m4
+++ b/m4/virt-compile-warnings.m4
@@ -177,6 +177,8 @@ AC_DEFUN([LIBVIRT_COMPILE_WARNINGS],[
     # with gl_MANYWARN_COMPLEMENT
     # So we have -W enabled, and then have to explicitly turn off...
     wantwarn="$wantwarn -Wno-sign-compare"
+    # We do "bad" function casts all the time for event callbacks
+    wantwarn="$wantwarn -Wno-cast-function-type"
 
     # GNULIB expects this to be part of -Wc++-compat, but we turn
     # that one off, so we need to manually enable this again