Fix and improve configuring code in makefile and script.

scripts/find_platform

@@ -2,20 +2,28 @@
 
 . inc/platform.sh
 
+# The backslash has to be put here 8 times: foctor two to get past the initial
+# shell quoting, another factor two because it is used in the replacement
+# string for sed, another factor two because the output of belows echo will be
+# used in the replacement text in the sed call in the makefile.  This yields
+# one backslash that can escape the single quote in the configured vimpager
+# script.
+AWK=$(echo "$AWK" | sed "s/'/'\\\\\\\\''/g")
+SED=$(echo "$SED" | sed "s/'/'\\\\\\\\''/g")
+
 echo \
-    bsd=$bsd \
-    cygwin=$cygwin \
-    freebsd=$freebsd \
-    linux=$linux \
-    msys=$msys \
-    netbsd=$netbsd \
-    openbsd=$openbsd \
-    osx=$osx \
-    solaris=$solaris \
-    win32=$win32 \
-    AWK=$AWK \
-    SED=$SED \
-    SED=$SED \
-    HEAD_SYNTAX=$HEAD_SYNTAX \
+    ${bsd:+bsd=$bsd} \
+    ${cygwin:+cygwin=$cygwin} \
+    ${freebsd:+freebsd=$freebsd} \
+    ${linux:+linux=$linux} \
+    ${msys:+msys=$msys} \
+    ${netbsd:+netbsd=$netbsd} \
+    ${openbsd:+openbsd=$openbsd} \
+    ${osx:+osx=$osx} \
+    ${solaris:+solaris=$solaris} \
+    ${win32:+win32=$win32} \
+    "AWK='$AWK'" \
+    "SED='$SED'" \
+    ${HEAD_SYNTAX:+HEAD_SYNTAX=$HEAD_SYNTAX} \
 
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