[rhel6] Fix missing /usr/bin/realpath.

gdb.spec

@@ -26,7 +26,7 @@ Version: 7.12
 
 # The release always contains a leading reserved number, start it at 1.
 # `upstream' is not a part of `name' to stay fully rpm dependencies compatible for the testing.
-Release: 36%{?dist}
+Release: 37%{?dist}
 
 License: GPLv3+ and GPLv3+ with exceptions and GPLv2+ and GPLv2+ with exceptions and GPL+ and LGPLv2+ and BSD and Public Domain and GFDL
 Group: Development/Debuggers
@@ -1352,7 +1352,11 @@ mkdir -p $RPM_BUILD_ROOT%{_prefix}/libexec
 mv -f $RPM_BUILD_ROOT%{_bindir}/gdb $RPM_BUILD_ROOT%{_prefix}/libexec/gdb
 %if 0%{?rhel:1} && 0%{?rhel} <= 6
 # RHEL-6: ln: invalid option -- 'r': https://bugzilla.redhat.com/show_bug.cgi?id=1384947
-ln -s $(realpath --relative-to=$RPM_BUILD_ROOT%{_bindir} $RPM_BUILD_ROOT%{_prefix}/libexec/gdb) $RPM_BUILD_ROOT%{_bindir}/gdb
+# RHEL-6 also does not have: /usr/bin/realpath
+ln -s $(
+  perl -le 'sub x{$_=$_[0];s{/+}{/}g;s{/$}{};return split "/";}@a=x shift;@b=x shift;while($a[0] eq $b[0]){shift @a;shift @b;}print join "/",map("..",@a),@b;' \
+    $RPM_BUILD_ROOT%{_bindir} $RPM_BUILD_ROOT%{_prefix}/libexec/gdb
+) $RPM_BUILD_ROOT%{_bindir}/gdb
 %else
 ln -s -r                                                 $RPM_BUILD_ROOT%{_prefix}/libexec/gdb  $RPM_BUILD_ROOT%{_bindir}/gdb
 %endif
@@ -1579,6 +1583,9 @@ then
 fi
 
 %changelog
+* Thu Jan 12 2017 Jan Kratochvil <jan.kratochvil@redhat.com> - 7.12-37.fc25
+- [rhel6] Fix missing /usr/bin/realpath.
+
 * Wed Jan 11 2017 Jan Kratochvil <jan.kratochvil@redhat.com> - 7.12-36.fc25
 - Update from FSF GDB 7.12 stable branch to snapshot: gdb-7.12.0.20170111