ENH: improve third-party make with central installations

- initial attempt for building CGAL as headers-only, and without
  gmp/mpfr

makeFFTW

@@ -29,7 +29,6 @@
 #     Build script for FFTW
 #
 #------------------------------------------------------------------------------
-
 # Get FFTW versions
 . $WM_PROJECT_DIR/etc/config.sh/functions
 unset -f _foamAddPath _foamAddLib _foamAddMan # get settings only
@@ -48,14 +47,12 @@ wmakeCheckPwd "$WM_THIRD_PARTY_DIR" || {
 }
 . etc/tools/ThirdPartyFunctions
 #------------------------------------------------------------------------------
-Script="${0##*/}"
-
 usage() {
     exec 1>&2
     while [ "$#" -ge 1 ]; do echo "$1"; shift; done
     cat<<USAGE
 
-usage: $Script [OPTION] [fftw-VERSION]
+usage: ${0##*/} [OPTION] [fftw-VERSION]
 options:
   -gcc              Force gcc/g++ instead of the values from \$WM_CC, \$WM_CXX
   -help
@@ -67,8 +64,7 @@ USAGE
     exit 1
 }
 #------------------------------------------------------------------------------
-
-# ensure configure gets the correct C/C++ compiler
+# Ensure configure gets the correct C/C++ compiler
 [ -n "$WM_CC" ]  && export CC="$WM_CC"
 [ -n "$WM_CXX" ] && export CXX="$WM_CXX"
 
@@ -98,14 +94,12 @@ done
 
 [ -n "$fftwPACKAGE" ] || die "The fftw-VERSION was not specified"
 
-# nothing to build
+# Nothing to build
 if _foamIsNone "$fftwPACKAGE"
 then
     echo "Using fftw-none (skip ThirdParty build of FFTW)"
     exit 0
-fi
-
-if _foamIsSystem "$fftwPACKAGE"
+elif _foamIsSystem "$fftwPACKAGE"
 then
     echo "Using fftw-system (skip ThirdParty build of FFTW)"
     exit 0
@@ -120,6 +114,7 @@ fi
 # - Third-Party builds into 'lib64'
 # - system is normally built into 'lib64'
 #
+#   FFTW_ARCH_PATH  : installation directory
 #   FFTW_SOURCE_DIR : location of the original sources
 
 FFTW_ARCH_PATH=$installBASE/$fftwPACKAGE
@@ -169,5 +164,4 @@ else
     }
 fi
 
-
 #------------------------------------------------------------------------------