• ran brew update and can still reproduce the problem?
• ran brew doctor, fixed all issues and can still reproduce the problem?
• ran brew gist-logs <formula> (where <formula> is the name of the formula that failed) and included the output link?
• if brew gist-logs didn't work: ran brew config and brew doctor and included their output with your issue?

What you were trying to do (and why)

install gettext package with its autoconf macros such as AM_ICONV

What happened (include command output)

its autoconf macros don't get installed to a location known to autotools,
even after running

brew link --force gettext

they remain in /usr/local/opt/gettext/share/aclocal/

What you expected to happen

the m4 files get installed in a location known to autotools, e.g.
/usr/local/share/aclocal/

Step-by-step reproduction instructions (by running brew install commands)

This would need a small autotools project to demonstrate an error message such as

configure:666666: error: possibly undefined macro: AM_ICONV

Running brew link --force gettext merely prints

Warning: Refusing to link macOS provided/shadowed software: gettext
If you need to have gettext first in your PATH run:
  echo 'export PATH="/usr/local/opt/gettext/bin:$PATH"' >> ~/.bash_profile

For compilers to find gettext you may need to set:
  export LDFLAGS="-L/usr/local/opt/gettext/lib"
  export CPPFLAGS="-I/usr/local/opt/gettext/include"

giving no clue regarding the fate of m4 files.
While one may go and manually create symlinks to the files in /usr/local/opt/gettext/share/aclocal/ at
/usr/local/share/aclocal/, this ought to happen automatically.