tools: hv: remove unnecessary link flag

The link flag pthread is not needed.
Signed-off-by: NWeibing Zhang <atheism.zhang@gmail.com>
Signed-off-by: NK. Y. Srinivasan <kys@microsoft.com>
Signed-off-by: NGreg Kroah-Hartman <gregkh@linuxfoundation.org>

tools/hv/Makefile

 # Makefile for Hyper-V tools
 
 CC = $(CROSS_COMPILE)gcc
-PTHREAD_LIBS = -lpthread
 WARNINGS = -Wall -Wextra
-CFLAGS = $(WARNINGS) -g $(PTHREAD_LIBS) $(shell getconf LFS_CFLAGS)
+CFLAGS = $(WARNINGS) -g $(shell getconf LFS_CFLAGS)
 
 CFLAGS += -D__EXPORTED_HEADERS__ -I../../include/uapi -I../../include