RFR(S): 8196992: Resolve disabled warnings for libdt_socket

[Chris Plummer]

Hello,

Please review the following:

https://bugs.openjdk.java.net/browse/JDK-8196992

diff --git a/make/lib/Lib-jdk.jdwp.agent.gmk 
b/make/lib/Lib-jdk.jdwp.agent.gmk
--- a/make/lib/Lib-jdk.jdwp.agent.gmk
+++ b/make/lib/Lib-jdk.jdwp.agent.gmk
@@ -43,7 +43,6 @@
      OPTIMIZATION := LOW, \
      CFLAGS := $(CFLAGS_JDKLIB) -DUSE_MMAP \
          $(LIBDT_SOCKET_CPPFLAGS), \
-    DISABLED_WARNINGS_gcc := shift-negative-value, \
      MAPFILE := $(TOPDIR)/make/mapfiles/libdt_socket/mapfile-vers, \
      LDFLAGS := $(LDFLAGS_JDKLIB) \
          $(call SET_SHARED_LIBRARY_ORIGIN), \

This change is undoing the makefile change done as part of JDK-8196985. 
The only warning that was turning up in libdt_socket code before 
JDK-8196985 was done has already been fixed by JDK-8196909. Thus no 
warnings need to be fixed.

After removing the above makefile code, I tested by building with the 
new toolchain. As a first test I undid the socketTransport.cpp fix from 
JDK-8196909 to verify that the new toolchain exposed the warning. Then I 
reverted socketTransport.cpp back to tip sources and saw no warnings 
with the new toolchain.

thanks,

Chris