Packages the distutils stdlib module as a standalone package,
```
377K distutils.data
221K distutils.data.br
19K distutils.js
```
to reduce the minimal pyodide size.

Part of #1542 

This also,
 - adds documentation on what's supported or not in the stdlib
 - makes a few changes to `pyodide_build/buildall.py` to be able to add such stdlib packages as a dependency in other packages (which didn't work before). For instance, until there is a release with https://github.com/pypa/packaging/pull/396 micropip has a dependency on distutils.
Unvendor distutils. Packages the distutils stdlib module as a standalone package,
```
377K distutils.data
221K distutils.data.br
19K distutils.js
```
to reduce the minimal pyodide size.

Part of #1542 

This also,
 - adds documentation on what's supported or not in the stdlib
 - makes a few changes to `pyodide_build/buildall.py` to be able to add such stdlib packages as a dependency in other packages (which didn't work before). For instance, until there is a release with https://github.com/pypa/packaging/pull/396 micropip has a dependency on distutils.
Add a missing extern in specfunc_wrappers.c

--- a/scipy/special/specfun_wrappers.c
+++ b/scipy/special/specfun_wrappers.c
@@ -35,6 +35,7 @@
 extern void F_FUNC(itairy,ITAIRY)(double*,double*,double*,double*,double*);
 extern void F_FUNC(e1xb,E1XB)(double*,double*);
 extern void F_FUNC(e1z,E1Z)(npy_cdouble*,npy_cdouble*);
+extern void F_FUNC(eixz,EIXZ)(npy_cdouble*,npy_cdouble*);
 extern void F_FUNC(eix,EIX)(double*,double*);
 extern void F_FUNC(cerror,CERROR)(npy_cdouble*,npy_cdouble*);
 extern void F_FUNC(stvh0,STVH0)(double*,double*);

Add a missing extern in specfunc_wrappers.c

--- a/scipy/special/specfun_wrappers.c
+++ b/scipy/special/specfun_wrappers.c
@@ -35,6 +35,7 @@
 extern void F_FUNC(itairy,ITAIRY)(double*,double*,double*,double*,double*);
 extern void F_FUNC(e1xb,E1XB)(double*,double*);
 extern void F_FUNC(e1z,E1Z)(npy_cdouble*,npy_cdouble*);
+extern void F_FUNC(eixz,EIXZ)(npy_cdouble*,npy_cdouble*);
 extern void F_FUNC(eix,EIX)(double*,double*);
 extern void F_FUNC(cerror,CERROR)(npy_cdouble*,npy_cdouble*);
 extern void F_FUNC(stvh0,STVH0)(double*,double*);
