Add option to specify the path to ncurses5-config

By default, gpsd's SConstruct looks in the PATH to find
ncurses5-config, which means that it finds our HOST_DIR
ncurses5-config. We add an option that allows to specify a custom path
to the ncurses5-config script.

Signed-off-by: Thomas Petazzoni <thomas.petazzoni@free-electrons.com>

Index: b/SConstruct
===================================================================
--- a/SConstruct
+++ b/SConstruct
@@ -172,6 +172,7 @@
     ("fixed_stop_bits",     0,             "fixed serial port stop bits"),
     ("target",              "",            "cross-development target"),
     ("sysroot",             "",            "cross-development system root"),
+    ("ncurses_config",      "",            "ncurses5-config path"),
     )
 for (name, default, help) in nonboolopts:
     opts.Add(name, help, default)
@@ -447,6 +448,11 @@
 else:
     pkg_config = lambda pkg: ['!%s --cflags --libs --static %s' %(env['PKG_CONFIG'], pkg, )]
 
+if env['ncurses_config']:
+    ncurses_config = env['ncurses_config']
+else:
+    ncurses_config = "ncurses5-config"
+
 # The actual distinction here is whether the platform has ncurses in the
 # base system or not. If it does, pkg-config is not likely to tell us
 # anything useful. FreeBSD does, Linux doesn't. Most likely other BSDs
@@ -455,8 +461,8 @@
 if env['ncurses']:
     if config.CheckPKG('ncurses'):
         ncurseslibs = pkg_config('ncurses')
-    elif config.CheckExecutable('ncurses5-config --version', 'ncurses5-config'):
-        ncurseslibs = ['!ncurses5-config --libs --cflags']
+    elif config.CheckExecutable('%s --version' % ncurses_config, 'ncurses5-config'):
+        ncurseslibs = ['!%s --libs --cflags' % ncurses_config]
     elif sys.platform.startswith('freebsd'):
         ncurseslibs= [ '-lncurses' ]
     elif sys.platform.startswith('openbsd'):