syscalls/sigpending02.c: Add libc sigpending() detection && reset sighandler_counter

1) bionic(Android libc) doesn't implement libc sigpending() currently,
   so we can skip it on Android by the detection.  Also add break to
   avoid potential compiler warnings.

2) Fix sigpending02 -i n by resetting sighandler_counter variable.

Reviewed-by: Petr Vorel <pvorel@suse.cz>
Signed-off-by: Xiao Yang <yangx.jy@cn.fujitsu.com>
diff --git a/configure.ac b/configure.ac
index 4208ae7..de12499 100644
--- a/configure.ac
+++ b/configure.ac
@@ -77,6 +77,7 @@
     readlinkat \
     renameat \
     renameat2 \
+    sigpending \
     splice \
     stime \
     syncfs \