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>

# mingw32 config options

# depends on EXPERIMENTAL

config KERNEL_mingw32

    select MINGW32

    help

      Build a toolchain targeting systems running Windows as host

choice

    bool

    prompt "Windows api version"

# Don't remove next line

# CT_INSERT_VERSION_BELOW

config W32API_V_3_14

    bool

    prompt "3.14"

config W32API_V_select

    bool

    prompt "Other version"

endchoice

config W32API_VERSION

    string

    prompt "W32 api version" if W32API_V_select

# Don't remove next line

# CT_INSERT_VERSION_STRING_BELOW

    default "3.14" if W32API_V_3_14

    help

      Enter the version number of the windows api files to use