got rid of std::invoke to avoid C++17 dependence

build/make.mingw64.test.py

@@ -16,7 +16,7 @@ builddir = "./build_mingw64"
 
 doinstall = False   #copies the build_output to the install dir when finished
 cc = "x86_64-w64-mingw32-g++" #compiler
-cflags = "-fPIC -O3 -std=c++17"
+cflags = "-fPIC -O3"
 libraries = "-l{}".format(libname)
 libdirs = "-L{} -L{}/lib -L{}/lib".format(builddir,commondir,depdir)
 linkerflags = "-static -static-libgcc -Wl,-rpath=."