CMake 3.11.1: CTest starts children with non-blocking pipes on Linux/sparc64

The tests WarnUnusedUnusedViaSet and WarnUnusedUnusedViaUnset are failing with cmake 3.11.1:

99% tests passed, 2 tests failed out of 488

Label Time Summary:
Label1    =   0.63 sec*proc (1 test)
Label2    =   0.63 sec*proc (1 test)

Total Test time (real) = 3814.47 sec

The following tests FAILED:
	178 - WarnUnusedUnusedViaSet (Failed)
	179 - WarnUnusedUnusedViaUnset (Failed)
Errors while running CTest

The kernel dmesg shows:

[844933.149371] cmsysTestProces[23903]: segfault at 4 ip 00000100000027d4 (rpc 00000100000027c0) sp 000007feffc900d1 error 1 in cmsysTestProcess[10000000000+a000]
[844933.153765] cmsysTestProces[23909]: segfault at 4 ip 00000100000027d4 (rpc 00000100000027c0) sp 000007feff86a0d1 error 1 in cmsysTestProcess[10000000000+a000]

They previously passed without problems in 3.10.2:

174/454 Test #181: WarnUnusedUnusedViaUnset ...............................   Passed    7.01 sec
181/454 Test #180: WarnUnusedUnusedViaSet .................................   Passed    7.75 sec

Full build logs for 3.11.1 and 3.10.2 available in 1 and 2.

Let me know if need access to a sparc64 porterbox for testing or anything else.

Since other architectures are not affected by this issue, this is most likely related to unaligned access to which SPARC is generally very sensitive to.