systemverilog-plugin: Update Makefile

Signed-off-by: Magdalena Andrys <mandrys@antmicro.com>

systemverilog-plugin/Makefile

diff --git a/systemverilog-plugin/Makefile b/systemverilog-plugin/Makefile
index af5320d..a72cb8f 100644
--- a/systemverilog-plugin/Makefile
+++ b/systemverilog-plugin/Makefile
@@ -22,7 +22,8 @@
           uhdmcommonfrontend.cc \
           uhdmsurelogastfrontend.cc \
           uhdmastreport.cc \
-          third_party/yosys/const2ast.cc
+          third_party/yosys/const2ast.cc \
+          third_party/yosys/simplify.cc
 
 # Directory to search for Surelog and UHDM libraries
 UHDM_INSTALL_DIR ?= /usr/local