Add configure script for Windows

Author: jeroen

DESCRIPTION

@@ -1,7 +1,7 @@
 Package: gifski
 Type: Package
 Title: Highest Quality GIF Encoder
-Version: 1.6.7
+Version: 1.7.0
 Authors@R: c(
     person("Jeroen", "Ooms", ,"jeroen@berkeley.edu", role = c("aut", "cre"),
       comment = c(ORCID = "0000-0002-4035-0289")),

configure.win

@@ -0,0 +1,14 @@
+#!/bin/sh
+# mimics: source ~/.cargo/env
+export PATH="$USERPROFILE/.cargo/bin:$PATH"
+
+# Write 'cargo' to Makevars
+VERSION=$(cargo --version)
+if [ $? -eq 0 ]; then
+  echo "Using `which cargo`"
+  echo "$VERSION"
+else
+  echo "Cargo not found. Falling back to static libraries"
+  cp -f src/Makevars.win.static src/Makevars.win
+fi
+exit 0

src/Makevars.win

@@ -3,13 +3,6 @@ LIBDIR = myrustlib/target/$(TARGET)/release
 STATLIB = $(LIBDIR)/libmyrustlib.a
 PKG_LIBS = -L$(LIBDIR) -lmyrustlib -lws2_32 -ladvapi32 -luserenv -ldbghelp -lbcrypt
 
-# These can also be set in ~/.cargo/config
-#export CARGO_TARGET_I686_PC_WINDOWS_GNU_LINKER=C:\\rtools40\\mingw$(WIN)\\bin\\gcc
-#export CC=$(CC)
-#export AR=$(AR)
-
-# This bypasses the exception stuff
-#export CARGO_TARGET_I686_PC_WINDOWS_GNU_RUSTFLAGS=-C panic=abort
 ifeq ($(R_COMPILED_BY),gcc 8.3.0)
 GCCPATH=$(subst C:\,/c/,$(RTOOLS40_HOME))/mingw$(WIN)/bin
 else
@@ -23,7 +16,7 @@ all: clean rustup
 $(SHLIB): $(STATLIB)
 
 $(STATLIB):
-ifeq ($(WIN),64) #hack for mxe-rtools42
+ifeq ($(WIN),64) #hack for missing libgcc_eh in mxe-rtools42
 	mkdir -p myrustlib/target/release/deps; echo '!<arch>' > myrustlib/target/release/deps/libgcc_eh.a
 endif
 	PATH="$(GCCPATH):$(USERPROFILE)\.cargo:$(PATH)" cargo build --target=$(TARGET) --release --manifest-path=myrustlib/Cargo.toml