fix incorrect EXPORT definition for Windows/x86_64 in boot-javahome.cpp

We should define EXPORT to be __declspec(dllexport) on Windows
regardless of architecture, not just non-x86_64 arches.  This fixes
errors to to embedded JAVA_HOME files not being found in openjdk-src
builds, e.g. lib/currency.data.
Merge pull request #225 from dicej/javahome

fix incorrect EXPORT definition for Windows/x86_64 in boot-javahome.cpp