icu: detect and add compiler symbol prefix to the assembly code

Some compilers, such as the Blackfin GNU compiler, prefix a character to any
C symbol in generated assembly code. If any assembly symbol is invoked
from C code, it needs to be prefixed as well.

Note: since autoreconf doesn't work with this package because automake
isn't used.

Fixes:
  http://autobuild.buildroot.net/results/c40a22814b405de2c5c75139cfc393c863ed4b81/



[Ryan: add information about why patching configure is ok]
[Ryan: add renaming of patches to be consistent with standard]

Signed-off-by: Sonic Zhang <sonic.zhang@analog.com>
Signed-off-by: Ryan Barnett <rjbarnet@rockwellcollins.com>
Signed-off-by: Peter Korsgaard <peter@korsgaard.com>