BUG #13499: building with xlc optimization level 5 can not initdb

The following bug has been logged on the website:

Bug reference: 13499
Logged by: Pete Lancashire
Email address: pete(at)petelancashire(dot)com
PostgreSQL version: 9.4.4
Operating system: AIX
Description:

oslevel -s 7100-03-03-1415
/usr/bin/ld: LD 7.1.3(4/1/14)
IBM XL C/C++ for AIX, V12.1 (5765-J02, 5725-C72)
Version: 12.01.0000.0000
Driver Version: 12.01(C/C++) Level: 120315
C Front End Version: 12.01(C/C++) Level: 120322
C++ Front End Version: 12.01(C/C++) Level: 120315
High-Level Optimizer Version: 12.01(C/C++) and 14.01(Fortran) Level: 120315
Low-Level Optimizer Version: 12.01(C/C++) and 14.01(Fortran) Level: 120321

PATH
/usr/local/bin:/usr/bin:/etc:/usr/sbin:/usr/ucb:/home/buildsw/bin:/usr/bin/X11:/sbin:.:/usr/vac/bin:/usr/vacpp/bin

OBJECT_MODE 64

CC xlc_r
CFLAGS -O5 -qmaxmem=-1 -qarch=pwr7 -qtune=pwr7 -qcache=auto
-I/usr/local/include

CXX xlc++_r
CXXFLAGS same as CFLAGS
LDPATH /usr/local/lib:/usr/lib

make check
$ cat initdb.log
Running in noclean mode. Mistakes will not be cleaned up.
The files belonging to this database system will be owned by user
"buildsw".
This user must also own the server process.

The database cluster will be initialized with locale "C".
The default database encoding has accordingly been set to "SQL_ASCII".
The default text search configuration will be set to "english".

Data page checksums are disabled.

creating directory
/home/buildsw/packages/postgresql-9.4.4_O5/src/test/regress/./tmp_check/data
... ok
creating subdirectories ... ok
selecting default max_connections ... 100
selecting default shared_buffers ... 128MB
selecting dynamic shared memory implementation ... posix
creating configuration files ... ok
creating template1 database in
/home/buildsw/packages/postgresql-9.4.4_O5/src/test/regress/./tmp_check/data/base/1
... FATAL: function "varchar_transform" does not exist
child process exited with exit code 1
initdb: data directory
"/home/buildsw/packages/postgresql-9.4.4_O5/src/test/regress/./tmp_check/data"
not removed at user's request