Don't use self.date unconditionally for program_out_of_date()

[jyn514]

This avoids unnecessary cache invalidations for programs not affected by
the stage0 version (which is everything except the stage0 compiler
itself).

The redundant invalidations weren't noticed until now because they only
showed up on stage0 bumps, at which point people are used to rebuilding
everything anyway. I noticed it in #79540
because I wasn't adding self.date to the stamp file (because I didn't realize it was necessary). Rather than
adding self.date I thought it was better to remove it from the cache key.

[rust-highfive]

r? @Mark-Simulacrum

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[rust-log-analyzer]

The job x86_64-gnu-llvm-9 failed! Check out the build log: (web) (plain)

Click to see the possible cause of the failure (guessed by this bot)

ERROR: test_dates_are_different (__main__.ProgramOutOfDate)
Return True when the dates are different
----------------------------------------------------------------------
Traceback (most recent call last):
  File "/checkout/src/bootstrap/bootstrap_test.py", line 87, in test_dates_are_different
    self.assertTrue(self.build.program_out_of_date(self.rustc_stamp_path))
TypeError: program_out_of_date() missing 1 required positional argument: 'key'
======================================================================
ERROR: test_same_dates (__main__.ProgramOutOfDate)
Return False both dates match
----------------------------------------------------------------------
----------------------------------------------------------------------
Traceback (most recent call last):
  File "/checkout/src/bootstrap/bootstrap_test.py", line 93, in test_same_dates
    self.assertFalse(self.build.program_out_of_date(self.rustc_stamp_path))
TypeError: program_out_of_date() missing 1 required positional argument: 'key'
======================================================================
ERROR: test_stamp_path_does_not_exists (__main__.ProgramOutOfDate)
Return True when the stamp file does not exists
----------------------------------------------------------------------
----------------------------------------------------------------------
Traceback (most recent call last):
  File "/checkout/src/bootstrap/bootstrap_test.py", line 81, in test_stamp_path_does_not_exists
    self.assertTrue(self.build.program_out_of_date(self.rustc_stamp_path))
TypeError: program_out_of_date() missing 1 required positional argument: 'key'
----------------------------------------------------------------------
Ran 16 tests in 0.006s

FAILED (errors=3)
FAILED (errors=3)
make: *** [check-bootstrap] Error 1
Makefile:49: recipe for target 'check-bootstrap' failed

[Mark-Simulacrum]

@bors r+

[bors]

📌 Commit 2f063cd has been approved by Mark-Simulacrum

[bors]

⌛ Testing commit 2f063cd with merge 9919ad6...

[bors]

☀️ Test successful - checks-actions
Approved by: Mark-Simulacrum
Pushing 9919ad6 to master...