powerpc(32) point/polygon regression failures on Debian Jessie

The point/polygon regression tests have started to fail on 32-bit
powerpc on Debian Jessie. So far I could reproduce the problem with
PostgreSQL 9.4.10+11 and 9.6.1, on several different machines. Debian
unstable is unaffected.

The failure looks like this:

https://buildd.debian.org/status/fetch.php?pkg=postgresql-9.6&arch=powerpc&ver=9.6.1-2~bpo8%2B1&stamp=1485184696&raw=0

******** build/src/test/regress/regression.diffs ********
*** /«PKGBUILDDIR»/build/../src/test/regress/expected/point.out Mon Oct 24 20:08:51 2016
--- /«PKGBUILDDIR»/build/src/test/regress/results/point.out Mon Jan 23 15:17:51 2017
***************
*** 125,131 ****
| (-3,4) | 5
| (-10,0) | 10
| (-5,-12) | 13
! | (10,10) | 14.142135623731
| (5.1,34.5) | 34.8749193547455
(6 rows)

--- 125,131 ----
| (-3,4) | 5
| (-10,0) | 10
| (-5,-12) | 13
! | (10,10) | 14.1421356237309
| (5.1,34.5) | 34.8749193547455
(6 rows)

***************
*** 150,157 ****
| (-5,-12) | (-10,0) | 13
| (-5,-12) | (0,0) | 13
| (0,0) | (-5,-12) | 13
! | (0,0) | (10,10) | 14.142135623731
! | (10,10) | (0,0) | 14.142135623731
| (-3,4) | (10,10) | 14.3178210632764
| (10,10) | (-3,4) | 14.3178210632764
| (-5,-12) | (-3,4) | 16.1245154965971
--- 150,157 ----
| (-5,-12) | (-10,0) | 13
| (-5,-12) | (0,0) | 13
| (0,0) | (-5,-12) | 13
! | (0,0) | (10,10) | 14.1421356237309
! | (10,10) | (0,0) | 14.1421356237309
| (-3,4) | (10,10) | 14.3178210632764
| (10,10) | (-3,4) | 14.3178210632764
| (-5,-12) | (-3,4) | 16.1245154965971
***************
*** 221,227 ****
| (-10,0) | (0,0) | 10
| (-10,0) | (-5,-12) | 13
| (-5,-12) | (0,0) | 13
! | (0,0) | (10,10) | 14.142135623731
| (-3,4) | (10,10) | 14.3178210632764
| (-5,-12) | (-3,4) | 16.1245154965971
| (-10,0) | (10,10) | 22.3606797749979
--- 221,227 ----
| (-10,0) | (0,0) | 10
| (-10,0) | (-5,-12) | 13
| (-5,-12) | (0,0) | 13
! | (0,0) | (10,10) | 14.1421356237309
| (-3,4) | (10,10) | 14.3178210632764
| (-5,-12) | (-3,4) | 16.1245154965971
| (-10,0) | (10,10) | 22.3606797749979

======================================================================

*** /«PKGBUILDDIR»/build/../src/test/regress/expected/polygon.out Mon Oct 24 20:08:51 2016
--- /«PKGBUILDDIR»/build/src/test/regress/results/polygon.out Mon Jan 23 15:17:51 2017
***************
*** 222,229 ****
'(2,2)'::point <-> '((0,0),(1,4),(3,1))'::polygon as inside,
'(3,3)'::point <-> '((0,2),(2,0),(2,2))'::polygon as near_corner,
'(4,4)'::point <-> '((0,0),(0,3),(4,0))'::polygon as near_segment;
! on_corner | on_segment | inside | near_corner | near_segment
! -----------+------------+--------+-----------------+--------------
! 0 | 0 | 0 | 1.4142135623731 | 3.2
(1 row)

--- 222,229 ----
'(2,2)'::point <-> '((0,0),(1,4),(3,1))'::polygon as inside,
'(3,3)'::point <-> '((0,2),(2,0),(2,2))'::polygon as near_corner,
'(4,4)'::point <-> '((0,0),(0,3),(4,0))'::polygon as near_segment;
! on_corner | on_segment | inside | near_corner | near_segment
! -----------+------------+--------+------------------+--------------
! 0 | 0 | 0 | 1.41421356237309 | 3.2
(1 row)

The 9.4.11 log contains the same point.out diff, but not polygon.out:
https://buildd.debian.org/status/fetch.php?pkg=postgresql-9.4&arch=powerpc&ver=9.4.11-0%2Bdeb8u1&stamp=1487517299&raw=0

Does that ring any bell? As Debian unstable is unaffected, it's likely
the toolchain to be blamed, but it worked for Debian Jessie before.

Christoph
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