perf jvmti: Link against tools/lib/ctype.h to have weak strlcpy()

perf jvmti: Link against tools/lib/ctype.h to have weak strlcpy()

The build of file libperf-jvmti.so succeeds but the resulting
object fails to load:

 # ~/linux/tools/perf/perf record -k mono -- java  \
      -XX:+PreserveFramePointer \
      -agentpath:/root/linux/tools/perf/libperf-jvmti.so \
       hog 100000 123450
  Error occurred during initialization of VM
  Could not find agent library /root/linux/tools/perf/libperf-jvmti.so
      in absolute path, with error:
      /root/linux/tools/perf/libperf-jvmti.so: undefined symbol: _ctype

Add the missing _ctype symbol into the build script.

Fixes: 79743bc927f6 ("perf jvmti: Link against tools/lib/string.o to have weak strlcpy()")
Signed-off-by: Thomas Richter <tmricht@linux.ibm.com>
Cc: Heiko Carstens <heiko.carstens@de.ibm.com>
Cc: Vasily Gorbik <gor@linux.ibm.com>
Link: http://lore.kernel.org/lkml/20191008093841.59387-1-tmricht@linux.ibm.com
Signed-off-by: Arnaldo Carvalho de Melo <acme@redhat.com>