Fix conversion from lower to upper case with Turkish locale

Fix conversion from lower to upper case with Turkish locale

Some locale settings let make fail or create wrong results
because tr '[:lower:]' '[:upper:]' which is used to convert
from lower to upper case depends on the locale.

With locale tr_TR.UTF-8, lower case 'i' is not converted to 'I'.
This results in wrong entries in config-host.h like these ones:

  #define CONFIG_QEMU_PREFiX "/usr/local"
  #define CONFIG_QEMU_BiNDiR "/usr/local/bin"

This problem was reported by Emre Ersin.

The same problem occurs when configure creates the target specific
files config-target.mak. They get wrong declarations:

TARGET_CRiS=y
TARGET_i386=y
TARGET_MiCROBLAZE=y
TARGET_MiPS64=y
TARGET_MiPS=y
TARGET_UNiCORE32=y

It is sufficient to restrict the conversion to the characters a-z.

Using this explicit range avoids the dependency on the locale
settings and is also shorter.

v2:
POSIX says that 'tr a-z' is unspecified outside of the POSIX
locale, so we must set LC_ALL=C to make sure that we are using
POSIX (hint from Eric Blake, thanks).

Signed-off-by: Stefan Weil <sw@weilnetz.de>
Signed-off-by: Blue Swirl <blauwirbel@gmail.com>