configure: Detect kcov support and introduce CONFIG_KCOV

kcov is kernel code coverage tracing tool. It requires kernel 4.4+
compiled with certain kernel options.

This patch checks if kcov header "sys/kcov.h" is present on build
machine, and stores the result in variable CONFIG_KCOV, meant to
be used in linux-user code related to the support for three ioctls
that were introduced at the same time as the mentioned header
(their definition was a part of the first version of that header).

Signed-off-by: Aleksandar Markovic <amarkovic@wavecomp.com>
Reviewed-by: Laurent Vivier <laurent@vivier.eu>
Message-Id: <1579214991-19602-11-git-send-email-aleksandar.markovic@rt-rk.com>
Signed-off-by: Laurent Vivier <laurent@vivier.eu>

configure

@@ -4761,6 +4761,12 @@ if compile_prog "" "" ; then
   syncfs=yes
 fi
 
+# check for kcov support (kernel must be 4.4+, compiled with certain options)
+kcov=no
+if check_include sys/kcov.h ; then
+    kcov=yes
+fi
+
 # Check we have a new enough version of sphinx-build
 has_sphinx_build() {
     # This is a bit awkward but works: create a trivial document and
@@ -6874,6 +6880,9 @@ fi
 if test "$syncfs" = "yes" ; then
   echo "CONFIG_SYNCFS=y" >> $config_host_mak
 fi
+if test "$kcov" = "yes" ; then
+  echo "CONFIG_KCOV=y" >> $config_host_mak
+fi
 if test "$inotify" = "yes" ; then
   echo "CONFIG_INOTIFY=y" >> $config_host_mak
 fi