Add build-win64-mingw32.sh (rebuild BDWGC for Win64 by mingw-w64)
Add build-linux-amd64/x86.sh (rebuild JCGO native binaries for Linux)
test-miscsrc-cygwin.sh: Define/use CC and SYST variables; wrap long lines
jcl.c: Fix pointer conversion GCC warnings in NewRawDataObject/GetRawData