I tried to restore the old behavior with the current find-debuginfo.sh script, with a change like this:

diff --git a/glibc.spec b/glibc.spec
index 5a388aed..6bb329bc 100644
--- a/glibc.spec
+++ b/glibc.spec
@@ -3692,16 +3692,26 @@ ls -l $RPM_BUILD_ROOT/usr/bin/getconf
 ls -l $RPM_BUILD_ROOT/usr/libexec/getconf
 eu-readelf -hS $RPM_BUILD_ROOT/usr/bin/getconf $RPM_BUILD_ROOT/usr/libexec/getconf/*
 
-find_debuginfo_args='--strict-build-id -g'
+find_debuginfo_args='--strict-build-id'
 %ifarch %{debuginfocommonarches}
-find_debuginfo_args="$find_debuginfo_args \
+# glibc-common contains no libraries, so everything can be stripped
+# (no -g).
+bash /usr/lib/rpm/find-debuginfo.sh $find_debuginfo_args \
   -l common.filelist -l utils.filelist -l nscd.filelist \
-  -p '.*/(sbin|libexec)/.*' \
-  -o debuginfocommon.filelist \
-  -l rpm.filelist -l nosegneg.filelist \
-"
+  -o debuginfocommon.filelist
 %endif
-eval /usr/lib/rpm/find-debuginfo.sh "$find_debuginfo_args" -o debuginfo.filelist
+
+# For the glibc package, we must only use -g for the main libraries.
+lib_pattern='.*/lib[^/]*/[^/]+(\.so\.[^/]+|\.so)$'
+grep -hE "$lib_pattern" rpm.filelist nosegneg.filelist \
+  > libonly-rpm.filelist
+grep -hEv "$lib_pattern" rpm.filelist nosegneg.filelist \
+  > nolib-rpm.filelist
+bash /usr/lib/rpm/find-debuginfo.sh $find_debuginfo_args -g \
+  -o libonly-debuginfo.filelist -l libonly-rpm.filelist
+bash /usr/lib/rpm/find-debuginfo.sh $find_debuginfo_args \
+  -o nolib-debuginfo.filelist -l nolib-rpm.filelist
+cat libonly-debuginfo.filelist nolib-debuginfo.filelist > debuginfo.filelist
 
 # List all of the *.a archives in the debug directory.
 list_debug_archives()

But I don't think invoking the script multiple times like this will work because find-debuginfo.sh is really designed to process all files and then handle the -l split afterwards.

Fixed with this patch:

diff --git a/glibc.spec b/glibc.spec
index d950a2a5..85bc411f 100644
--- a/glibc.spec
+++ b/glibc.spec
@@ -1677,6 +1677,9 @@ BuildRequires: systemd
 # the required semantics.
 BuildRequires: gcc >= 4.8.5-25
 
+# This RPM version introduced --g-libs.
+BuildRequires: rpm-build >= 4.11.3-38.el7
+
 %define enablekernel 2.6.32
 Conflicts: kernel < %{enablekernel}
 %define target %{_target_cpu}-redhat-linux
@@ -3812,7 +3815,7 @@ ls -l $RPM_BUILD_ROOT/usr/bin/getconf
 ls -l $RPM_BUILD_ROOT/usr/libexec/getconf
 eu-readelf -hS $RPM_BUILD_ROOT/usr/bin/getconf $RPM_BUILD_ROOT/usr/libexec/getconf/*
 
-find_debuginfo_args='--strict-build-id -g'
+find_debuginfo_args='--strict-build-id --g-libs'
 %ifarch %{debuginfocommonarches}
 find_debuginfo_args="$find_debuginfo_args \
   -l common.filelist -l utils.filelist -l nscd.filelist \

Verified,

glibc-2.17-290.el7 contains stripped binaries, it also produces stripped binaries during rpmbuild -bb

Since the problem described in this bug report should be
resolved in a recent advisory, it has been closed with a
resolution of ERRATA.

For information on the advisory, and where to find the updated
files, follow the link below.

If the solution does not work for you, open a new bug report.

https://access.redhat.com/errata/RHSA-2019:2118

*** Bug 1982316 has been marked as a duplicate of this bug. ***