Some fixes for rtools42

Author: jeroen

src/Makevars.win

@@ -12,14 +12,18 @@ PKG_LIBS = -L$(LIBDIR) -lmyrustlib -lws2_32 -ladvapi32 -luserenv -ldbghelp -lbcr
 #export CARGO_TARGET_I686_PC_WINDOWS_GNU_RUSTFLAGS=-C panic=abort
 ifeq ($(R_COMPILED_BY),gcc 8.3.0)
 GCCPATH=$(subst C:\,/c/,$(RTOOLS40_HOME))/mingw$(WIN)/bin
+else
+export CARGO_TARGET_X86_64_PC_WINDOWS_GNU_LINKER=gcc
+GCCPATH=$(subst C:\,/c/,$(RTOOLS42_HOME))/x86_64-w64-mingw32.static.posix/bin
 endif
 
 all: clean rustup
 
 $(SHLIB): $(STATLIB)
 
 $(STATLIB):
-	PATH="$(GCCPATH):$(PATH)" cargo build --target=$(TARGET) --release --manifest-path=myrustlib/Cargo.toml
+	mkdir -p myrustlib/target/release/deps; echo '!<arch>' > myrustlib/target/release/deps/libgcc_eh.a #hack for mxe-rtools42
+	PATH="$(GCCPATH):$(USERPROFILE)\.cargo:$(PATH)" cargo build --target=$(TARGET) --release --manifest-path=myrustlib/Cargo.toml
 
 clean:
 	rm -Rf $(SHLIB) $(STATLIB) $(OBJECTS) myrustlib/target