shtool is overkill here and usually not done by us; use a simpler construct which is already sufficient for our use

mtr/mtr.spec

@@ -63,10 +63,7 @@ AutoReqProv:  no
     %patch -p0
 
 %build
-    %{l_shtool} echo \
-        'ac_cv_lib_termcap_tgetent=${ac_cv_lib_termcap_tgetent=no}' \
-        > config.cache
-
+    echo 'ac_cv_lib_termcap_tgetent=no' >config.cache
     CC="%{l_cc}" \
     CFLAGS="%{l_cflags -O}" \
     CPPFLAGS="%{l_cppflags}" \