alpha: cpow math testsuite failures with GCC 9

[Florian Weimer]

* Aurelien Jarno:

> Here is the detailed failure for math/test-double-cpow:
>
> | FAIL: math/test-double-cpow
> | original exit status 1
> | testing double (without inline functions)
> | Failure: Test: Real part of: cpow_downward (0x2p+0 + +0 i, 0xap+0 + +0 i)
> | Result:
> |  is:          1.0239999999999989e+03   0x1.ffffffffffff7p+9
> |  should be:   1.0240000000000000e+03   0x1.0000000000000p+10
> |  difference:  1.0231815394945442e-12   0x1.2000000000000p-40
> |  ulp       :  4.5000
> |  max.ulp   :  2.0000
> | Maximal error of real part of: cpow_downward
> |  is      : 5 ulp
> |  accepted: 2 ulp
> | Maximal error of imaginary part of: cpow_downward
> |  is      : 1 ulp
> |  accepted: 1 ulp
> | Failure: Test: Real part of: cpow_towardzero (0x2p+0 + +0 i, 0xap+0 + +0 i)
> | Result:
> |  is:          1.0239999999999989e+03   0x1.ffffffffffff7p+9
> |  should be:   1.0240000000000000e+03   0x1.0000000000000p+10
> |  difference:  1.0231815394945442e-12   0x1.2000000000000p-40
> |  ulp       :  4.5000
> |  max.ulp   :  2.0000
> | Maximal error of real part of: cpow_towardzero
> |  is      : 5 ulp
> |  accepted: 2 ulp
> | Maximal error of imaginary part of: cpow_towardzero
> |  is      : 1 ulp
> |  accepted: 1 ulp
> | 
> | Test suite completed:
> |   50 test cases plus 46 tests for exception flags and
> |     46 tests for errno executed.
> |   4 errors occurred.

These failures look pretty much like what we accept on other targets.
You should simply regenerate the ulps file, see “make reben-ulps” in
math/README.libm-test.  Post the patch before committing it if you still
feel unsure about this.

Thanks,
Florian