The default `strip` invocation tries to strip global symbols from the
library, and refuses because those are indirect symbol table
references.

The latter doesn't exist on Darwin (and, presumably, other targets as
well). This change allows emacsGcc from emacs-overlay to attempt to
build where previously, the derivation would error out.

Turns out that libgccjit gets installed as a .so file, which the gcc
builder.sh didn't change: It only touched .dylib files; that means
that anything linking in libgccjit.so would receive an "Image not
found" error at load time.

With this change, we invoke `install_name_tool` on .so files too,
adjusting their dynamic linker ID, so that they too can be found.

This changes PATH such that the correct linker can be found to
construct .eln files at runtime.

Since Darwin's linker does not understand LIBRARY_PATH, we have to set
the library path as explicit linker flags: This requires a very recent
feature/native-comp emacs revision, but it runs on Darwin and
correctly compiles files at runtime.

It's not necessary to use strip -x otherwise, so let's just use it for
the JIT library.

This is the portable way to address the system-appropriate libc,
better than conditionalizing by (darwin/GNU) system or using either
one.

This way, we don't have to drag clang or binutils/binutils-wrapped
into the emacs closure, and can instead rely on using the correct one
for the platform we're running on.

Co-authored-by: Matthew Bauer <mjbauer95@gmail.com>

The -B flag to gcc (and libgccjit) allows us to specify where it can
find things it needs to correctly compile code (both programs and
libraries) without adjusting any environmental flags: So, no need to
wrap the program for a PATH entry containing binutils, and no need to
explicitly pass a linker path anymore.

The -B flag to gcc (and libgccjit) allows us to specify where it can
find things it needs to correctly compile code (both programs and
libraries) without adjusting any environmental flags: So, no need to
wrap the program for a PATH entry containing binutils, and no need to
explicitly pass a linker path anymore.

emacs: Make gccemacs build on darwin