#C, 37 byte source, 4,294,975,927 byte executable
This simply defines a large global array and initialises its first element. This causes GCC to store the entire array in the resulting executable.
Because this array is bigger than 2GB, we need to provide the -mcmodel=medium flag to GCC. The extra 15 bytes are included in the score, as per the rules.
a[1<<30]={1};main(){}; Compile with:
gcc -mcmodel=medium cbomb.c -o cbomb