Commit f14cc75 accidentally added a const when grepping for assignments
to `std.builtin.Type.StructField.default_value`, however when looking
into it further, I noticed that even though this default_value field is
emitted into the .data section, the value it points to is actually
emitted into the .rodata section, so it seems correct to use const here.
Finishes cleanups that I started in other commits in this branch.
* Use common.linkage for all exports instead of redoing the logic in
each file.
* Remove pointless `@setRuntimeSafety` calls.
* Avoid redundantly exporting multiple versions of functions. For
example, if PPC wants `ceilf128` then don't also export `ceilq`;
similarly if ARM wants `__aeabi_ddiv` then don't also export
`__divdf3`.
* Use `inline` for helper functions instead of making inline calls at
callsites.
stage2: change logic for detecting whether the main package is inside
the std package. Previously it relied on realpath() which is not portable.
This uses resolve() which is how imports already work.
* stage2: fix cleanup bug when creating Module
* flatten lib/std/special/* to lib/*
- this was motivated by making main_pkg_is_inside_std false for
compiler_rt & friends.
* rename "mini libc" to "universal libc"
