Move most flags from module_codegen to new_context #1590

Job	Run time
build (libgccjit_without_int128.so, master-without-128bit-integers)	8m 32s
build (libgccjit.so, master)	8m 46s
build (libgccjit12.so, gcc12, --no-default-features, TEST_FLAGS='-Cpanic=abort -Zpanic-abort-test...	1m 26s
success_failures	3s
	18m 47s

Provide feedback