Set JULIA_HOME?

[samoconnor]

In a statically compiled program Base.julia_cmd() seems to use the directory of the static executable as the path to the julia executable.

To work around this I've added -DJULIA_HOME=$JULIA_HOME to the gcc command line in juliac.jl. and setenv("JULIA_HOME", TOSTRING(JULIA_HOME), 0); in the main() function in program.c.

This causes the statically compiled program to have the same JULIA_HOME as the compile-time julia.

[vtjnash]

related: JuliaLang/julia#20899