x/website: update /doc/install/source page after GO386 changes

[ALTree]

The Installing Go from source page says (in the section dedicated to Env Variables):

$GO386 (for 386 only, default is auto-detected if built on either 386 or amd64, 387 otherwise)

This controls the code generated by gc to use either the 387 floating-point unit (set to 387) or SSE2 instructions (set to sse2) for floating point computations.

• GO386=387: use x87 for floating point operations; should support all x86 chips (Pentium MMX or later).
• GO386=sse2: use SSE2 for floating point operations; has better performance than 387, but only available on Pentium 4/Opteron/Athlon 64 or later.

The section should be updated to reflect the planned 1.16 deprecation of 387, and the softfloat support.

cc @dmitshur

[dmitshur]

Thanks for spotting this @ALTree.

@randall77 Would you like to send a CL for this? The file that needs to be updated is in x/website, here. (There's also an old copy of it in the main repo, but that needs to be deleted; I re-opened #40496 (comment) for that.)

Edit: Since the file is in x/website, we should not submit the CL until Go 1.16 comes out. Can add wait-release hashtag to it.

[gopherbot]

Change https://golang.org/cl/260757 mentions this issue: doc: update install docs for 387->softfloat transition

[gopherbot]

Change https://golang.org/cl/260700 mentions this issue: content/static/doc: update install docs for 387->softfloat transition

[dmitshur]

Reopening because the x/website CL was reverted in CL 261557. x/website needs to be modified when Go 1.16 is released. I'll move this to Go 1.17 milestone with early-in-cycle.