Request the ability to set the XCOFF header timestamps generated by the linker to NULL

It is presumed the -bdbg:dbopt9 flag option sufficiently addresses this RFE. Please resubmit the RFE if this is not the case.

The -bdbg:dbopt9 flag can be used to write a zero in the timestamp field. IBM plans to explore documentation updates to cover this option.

Please give this a try and let us know if this meets your needs.

Here is an example:

$ ld -o main /lib/crt0.o main.o helper.o -lc -bdbg:dbopt9
$ ls -al
-rwx------ 1 tstuser tstuser 6309 Jan 25 17:29 main
-rwx------ 1 tstuser tstuser 119 May 5 2021 main.c
-rw------- 1 tstuser tstuser 2338 Jan 25 16:31 main.o
$ shasum main
69225dd518f1acc34df37bdf2d8f9176daf14062 main

$ rm main

$ ld -o main /lib/crt0.o main.o helper.o -lc -bdbg:dbopt9
$ ls -al
total 104
-rwx------ 1 tstuser tstuser 6309 Jan 25 17:30 main
-rwx------ 1 tstuser tstuser 119 May 5 2021 main.c
-rw------- 1 tstuser tstuser 2338 Jan 25 16:31 main.o
$ shasum main
69225dd518f1acc34df37bdf2d8f9176daf14062 main

When you remove the -bdbg:dbopt9 flag and re-link:
$ rm main
$ ld -o main /lib/crt0.o main.o helper.o -lc
$ shasum main
f73f61889ee05440e0492c9ee9ac55a8acf3772e main

A suggestion is to use a binary editor to zero out the timestamp field.
IBM has evaluated the priority of this enhancement proposal relative to other future product content and determined that this RFE will not be pursued for a future product release

I think you need to try the recommendation in the XLCv11 documentation first:

It is recommended that you use the -qmkshrobj compiler option instead of the makeC++SharedLib command. Among the advantages to using this option are the automatic handling of link-time C++ template instantiation (using either the template include directory or the template registry), and compatibility with the -O5 option.

See https://www.ibm.com/docs/en/xl-c-and-cpp-aix/11.1.0?topic=utilities-creating-shared-library-makecsharedlib-utility