scripts: remove . from $PATH

Add CT_SanitizePath function which removes entries referring to ., /tmp
and non-existing directories from $PATH, and call it early in the
build script.

If . is in PATH, gcc-4.4.4 build breaks:

[ALL ] checking what assembler to use...
/tmp/build/targets/arm-unknown-linux-uclibcgnueabi/build/gcc-core-static/arm-unknown-linux-uclibcgnueabi/bin/as
...
[ALL ] config.status: creating as

i.e. "as" is supposed to be the arm-unknown-linux-uclibcgnueabi cross assembler,
but config.status creates a local "as" script which is calling the
host assembler.

Signed-off-by: Johannes Stezenbach <js@sig21.net>
[Yann E. MORIN: style fixes + explanations]
Signed-off-by: "Yann E. MORIN" <yann.morin.1998@anciens.enib.fr>
(transplanted from 20dd8cef1c8adff0aa3e78ae6d7acfbc45ed5a83)

diff -dur strace-4.5.16.orig/net.c strace-4.5.16/net.c

--- strace-4.5.16.orig/net.c	2006-12-13 20:57:23.000000000 +0100

+++ strace-4.5.16/net.c	2007-07-14 19:29:36.000000000 +0200

@@ -800,8 +800,12 @@

 #ifdef SOL_PACKET

 static const struct xlat sockpacketoptions[] = {

+#if defined(PACKET_ADD_MEMBERSHIP)

 	{ PACKET_ADD_MEMBERSHIP,	"PACKET_ADD_MEMBERSHIP"	},

+#endif

+#if defined(PACKET_DROP_MEMBERSHIP)

 	{ PACKET_DROP_MEMBERSHIP,	"PACKET_DROP_MEMBERSHIP"},

+#endif

 #if defined(PACKET_RECV_OUTPUT)

 	{ PACKET_RECV_OUTPUT,		"PACKET_RECV_OUTPUT"	},

 #endif