drd/drd_pthread_intercepts: Add a workaround for what is probably a compiler bug

drd/drd_pthread_intercepts: Add a workaround for what is probably a compiler bug

Without this patch drd produces incorrect output for some test cases. It
seems like without this patch an incorrect value is passed as the sixth
argument of VALGRIND_DO_CLIENT_REQUEST_STMT(VG_USERREQ__POST_SEM_OPEN, ...):

$ ./vg-in-place --tool=drd --traemaphore=yes drd/tests/sem_open -m -p
drd, a thread error detector
Copyright (C) 2006-2017, and GNU GPL'd, by Bart Van Assche.
Using Valgrind-3.16.0.GIT and LibVEX; rerun with -h for copyright info
Command: drd/tests/sem_open -m -p

[1] sem_open      0x4029000 name /drd-sem-open-test-27725 oflag 0xc0 mode 0600 value 0
s_d1 = 1 (should be 1)
[2] sem_wait      0x4029000 value 0 -> 4294967295
Thread 2:
Invalid semaphore: semaphore 0x4029000
   at 0x484ADC7: sem_wait_intercept (drd_pthread_intercepts.c:1436)
   by 0x484ADC7: sem_wait@* (drd_pthread_intercepts.c:1441)
   by 0x4014A9: thread_func (sem_open.c:114)
   by 0x483FEA6: vgDrd_thread_wrapper (drd_pthread_intercepts.c:449)
   by 0x4886EF9: start_thread (in /lib64/libpthread-2.31.so)
   by 0x499F3BE: clone (in /lib64/libc-2.31.so)
semaphore 0x4029000 was first observed at:
   at 0x484A395: sem_open_intercept (drd_pthread_intercepts.c:1403)
   by 0x484A395: sem_open (drd_pthread_intercepts.c:1409)
   by 0x4012CE: main (sem_open.c:63)

[2] sem_post      0x4029000 value 4294967295 -> 0
[1] sem_wait      0x4029000 value 0 -> 4294967295
Thread 1:
Invalid semaphore: semaphore 0x4029000
   at 0x484ADC7: sem_wait_intercept (drd_pthread_intercepts.c:1436)
   by 0x484ADC7: sem_wait@* (drd_pthread_intercepts.c:1441)
   by 0x40139D: main (sem_open.c:90)
semaphore 0x4029000 was first observed at:
   at 0x484A395: sem_open_intercept (drd_pthread_intercepts.c:1403)
   by 0x484A395: sem_open (drd_pthread_intercepts.c:1409)
   by 0x4012CE: main (sem_open.c:63)

Conflicting load by thread 1 at 0x00404108 size 8
   at 0x40139E: main (sem_open.c:91)
Allocation context: BSS section of /home/bart/software/valgrind.git/drd/tests/sem_open
Other segment start (thread 2)
   (thread finished, call stack no longer available)
Other segment end (thread 2)
   (thread finished, call stack no longer available)

Conflicting store by thread 1 at 0x00404108 size 8
   at 0x4013B2: main (sem_open.c:91)
Allocation context: BSS section of /home/bart/software/valgrind.git/drd/tests/sem_open
Other segment start (thread 2)
   (thread finished, call stack no longer available)
Other segment end (thread 2)
   (thread finished, call stack no longer available)

[1] sem_post      0x4029000 value 4294967295 -> 0
s_d2 = 2 (should be 2)
s_d3 = 5 (should be 5)
[1] sem_close     0x4029000 value 0

For lists of detected and suppressed errors, rerun with: -s
ERROR SUMMARY: 4 errors from 4 contexts (suppressed: 18 from 8)