./configure: add link check for nss-smartcard

Current './configure --static && make' fails for me:

    LINK  qemu-nbd
    /usr/lib/gcc/x86_64-pc-linux-gnu/4.5.3/../../../../x86_64-pc-linux-gnu/bin/ld: cannot find -lssl3
    /usr/lib/gcc/x86_64-pc-linux-gnu/4.5.3/../../../../x86_64-pc-linux-gnu/bin/ld: cannot find -lsmime3
    /usr/lib/gcc/x86_64-pc-linux-gnu/4.5.3/../../../../x86_64-pc-linux-gnu/bin/ld: cannot find -lnssutil3
    /usr/lib/gcc/x86_64-pc-linux-gnu/4.5.3/../../../../x86_64-pc-linux-gnu/bin/ld: cannot find -lnss3
    /usr/lib/gcc/x86_64-pc-linux-gnu/4.5.3/../../../../x86_64-pc-linux-gnu/bin/ld: cannot find -lplds4
    /usr/lib/gcc/x86_64-pc-linux-gnu/4.5.3/../../../../x86_64-pc-linux-gnu/bin/ld: cannot find -lplc4
    /usr/lib/gcc/x86_64-pc-linux-gnu/4.5.3/../../../../x86_64-pc-linux-gnu/bin/ld: cannot find -lnspr4

My system does not provide static libraries for nss, so
fix autoconfiguration by link checking.
Signed-off-by: NSergei Trofimovich <slyfox@gentoo.org>
CC: qemu-trivial <qemu-trivial@nongnu.org>
Signed-off-by: NAnthony Liguori <aliguori@us.ibm.com>

configure

@@ -2528,11 +2528,16 @@ if test "$smartcard" != "no" ; then
     smartcard_cflags=""
     # TODO - what's the minimal nss version we support?
     if test "$smartcard_nss" != "no"; then
-        if $pkg_config --atleast-version=3.12.8 nss >/dev/null 2>&1 ; then
+      cat > $TMPC << EOF
+#include <pk11pub.h>
+int main(void) { PK11_FreeSlot(0); return 0; }
+EOF
+        smartcard_cflags="-I\$(SRC_PATH)/libcacard"
+        libcacard_libs=$($pkg_config --libs nss 2>/dev/null)
+        libcacard_cflags=$($pkg_config --cflags nss 2>/dev/null)
+        if $pkg_config --atleast-version=3.12.8 nss >/dev/null 2>&1 && \
+          compile_prog "$smartcard_cflags $libcacard_cflags" "$libcacard_libs"; then
             smartcard_nss="yes"
-            smartcard_cflags="-I\$(SRC_PATH)/libcacard"
-            libcacard_libs=$($pkg_config --libs nss 2>/dev/null)
-            libcacard_cflags=$($pkg_config --cflags nss 2>/dev/null)
             QEMU_CFLAGS="$QEMU_CFLAGS $smartcard_cflags $libcacard_cflags"
             LIBS="$libcacard_libs $LIBS"
         else