Set VDF_MODE according to the passed env var, and make it 1 on the CI test workflows.

Author: AmineKhaldi

.github/workflows/test.yaml

@@ -36,13 +36,14 @@ jobs:
       run: |
         sudo apt-get install libgmp-dev libboost-python-dev libpython3-dev libboost-system-dev build-essential -y
         cd src
-        make ${{ matrix.config }} -f Makefile.vdf-client
+        VDF_MODE=1 make ${{ matrix.config }} -f Makefile.vdf-client
 
     - name: Build vdf-client on Mac
       if: startsWith(matrix.os, 'mac')
       run: |
         brew install boost
         cd src
+        # TODO: Are we expected to fail to compile with VDF_MODE=1 on macOS
         make ${{ matrix.config }} -f Makefile.vdf-client
 
     - name: Test vdf-client

src/Makefile.vdf-client

@@ -8,7 +8,9 @@ endif
 
 LDFLAGS += -flto $(NOPIE) -g
 LDLIBS += -lgmpxx -lgmp -lboost_system -pthread
-CXXFLAGS += -flto -std=c++1z -D VDF_MODE=0 -D FAST_MACHINE=1 -pthread $(NOPIE) -fvisibility=hidden
+
+VDF_MODE ?= 0
+CXXFLAGS += -flto -std=c++1z -D VDF_MODE=$(VDF_MODE) -D FAST_MACHINE=1 -pthread $(NOPIE) -fvisibility=hidden
 ifeq ($(UNAME),Darwin)
 CXXFLAGS += -D CHIAOSX=1
 endif