I had a go at compiling cmake, so many ar related problems. I can understand why you tried something else.
Apparently the xlC-16 runtime of libc++.rte isn't sufficient (
https://www.ibm.com/support/pages/node/795548).
/root/cpp-runtime]ls -l
total 53660
-rwxr-xr-x 1 313661 758677 2392735 Jan 15 2019 LicenseAgreement.pdf
-rw-r--r-- 1 313661 758677 4799 Jan 15 2019 README
-rw-r--r-- 1 313661 758677 4990976 Jan 16 2019 libc++.rte
-rwxr-xr-x 1 313661 758677 248394 Jan 15 2019 license.pdf
-rwxr-xr-x 1 313661 758677 7670 Jan 15 2019 notices
-rw-r--r-- 1 313661 758677 22528 Jan 16 2019 xlC.adt
-rw-r--r-- 1 313661 758677 38982656 Jan 16 2019 xlC.aix61
-rw-r--r-- 1 313661 758677 14336 Jan 16 2019 xlC.msg.Ja_JP
-rw-r--r-- 1 313661 758677 13312 Jan 16 2019 xlC.msg.en_US
-rw-r--r-- 1 313661 758677 14336 Jan 16 2019 xlC.msg.ja_JP
-rw-r--r-- 1 313661 758677 4024320 Jan 16 2019 xlC.rte
-rw-r--r-- 1 313661 758677 4074496 Jan 16 2019 xlsmp.aix61.rte
-rw-r--r-- 1 313661 758677 11264 Jan 16 2019 xlsmp.msg.EN_US.rte
-rw-r--r-- 1 313661 758677 11264 Jan 16 2019 xlsmp.msg.En_US.rte
-rw-r--r-- 1 313661 758677 11264 Jan 16 2019 xlsmp.msg.JA_JP.rte
-rw-r--r-- 1 313661 758677 9216 Jan 16 2019 xlsmp.msg.Ja_JP.rte
-rw-r--r-- 1 313661 758677 8192 Jan 16 2019 xlsmp.msg.ZH_CN.rte
-rw-r--r-- 1 313661 758677 7168 Jan 16 2019 xlsmp.msg.Zh_CN.rte
-rw-r--r-- 1 313661 758677 11264 Jan 16 2019 xlsmp.msg.en_US.rte
-rw-r--r-- 1 313661 758677 9216 Jan 16 2019 xlsmp.msg.ja_JP.rte
-rw-r--r-- 1 313661 758677 7168 Jan 16 2019 xlsmp.msg.zh_CN.rte
-rw-r--r-- 1 313661 758677 30720 Jan 16 2019 xlsmp.rte
/opt/bin/cmake --version
Could not load program /opt/bin/cmake:
Symbol resolution failed for cmake because:
Symbol _ZTv0_n12_NSt3__113basic_istreamIcNS_11
char_traitsIcEEED0Ev (number 552) is not exported from dependent
module /usr/lib/libc++.a(shr.o).
Symbol _ZTv0_n12_NSt3__113basic_istreamIcNS_11
char_traitsIcEEED1Ev (number 553) is not exported from dependent
module /usr/lib/libc++.a(shr.o).
Symbol _ZTv0_n12_NSt3__113basic_ostreamIcNS_11
char_traitsIcEEED0Ev (number 554) is not exported from dependent
module /usr/lib/libc++.a(shr.o).
Symbol _ZTv0_n12_NSt3__113basic_ostreamIcNS_11
char_traitsIcEEED1Ev (number 555) is not exported from dependent
module /usr/lib/libc++.a(shr.o).
Symbol _ZTv0_n12_NSt3__114basic_iostreamIcNS_1
1char_traitsIcEEED0Ev (number 556) is not exported from dependent
module /usr/lib/libc++.a(shr.o).
Symbol _ZTv0_n12_NSt3__114basic_iostreamIcNS_1
1char_traitsIcEEED1Ev (number 557) is not exported from dependent
module /usr/lib/libc++.a(shr.o).
IBM_XL_CPP_UTILITIES_V16.1.0.0_AIX.tar.
Z didn't help.