Bug 1413593 - Add win32 cross compilation config for geckodriver. r?jgraham When cross-compiling geckodriver for i686-pc-windows-gnu from Linux x86-64, this custom cargo configuration is needed. It specifies the linker to use as well as a rustc flag for disabling backtraces on panic, as far as I gather. Neither of these options are necessary, of course, when we start releasing geckodriver from Taskcluster, because we will then not rely on cross-compilation. MozReview-Commit-ID: 6q7wIBNrCHB

new file mode 100644
--- /dev/null
+++ b/testing/geckodriver/.cargo/config
@@ -0,0 +1,3 @@
+[target.i686-pc-windows-gnu]
+linker = "i686-w64-mingw32-gcc"
+rustflags = "-C panic=abort"