cc/gcc: remove 'sub-level' version form symbols

Now we use defconfig files to store the samples, we have to be a bit more
conservatives in the symbols names, so as to avoid gigantic version bumps
when updating sub-level versions from a package.

For example (using fictitious versions):
- in crosstool-NG 1.17.0, we choose:
- latest gcc is gcc-linaro-4.7-2012.10, which is the default for the
choice in the menuconfig
- gcc-linaro-4.6-2012.10 is selected
- so, sample has an explicit symbol for the selected gcc version, as it
is not the default
- we update to crosstool-NG 1.18.0:
- latest gcc version is gcc-linaro-4.7-2013.01
- gcc-linaro-46 has been updated to gcc-linaro-4.6-2013.01
- as the sample now has no *valid* symbol to set the gcc version, the
default is used, while we would have expected to still use the 4.6
release from linaro, not the 4.7

Get rid of sub-level (ie. the third digit sequence in versions) from the
symbols for linaro versions.

Signed-off-by: "Yann E. MORIN" <yann.morin.1998@free.fr>

 # strace

 ## depends on ! BACKEND

 choice

     bool

     prompt "strace version"

 # Don't remove next line

 # CT_INSERT_VERSION_BELOW

 config STRACE_V_4_6

     bool

     prompt "4.6"

     depends on CONFIGURE_has_xz

 config STRACE_V_4_5_20

     bool

     prompt "4.5.20"

 config STRACE_V_4_5_19

     bool

     prompt "4.5.19"

 config STRACE_V_4_5_18

     bool

     prompt "4.5.18"

 endchoice

 config STRACE_VERSION

     string

 # Don't remove next line

 # CT_INSERT_VERSION_STRING_BELOW

     default "4.6" if STRACE_V_4_6

     default "4.5.20" if STRACE_V_4_5_20

     default "4.5.19" if STRACE_V_4_5_19

     default "4.5.18" if STRACE_V_4_5_18