Import IRSTLM patching script from Kaldi

On Mac OS X, when running the ./extras/install_irstlm.sh script in XCode 9 (works fine in XCode 8):

libtool: compile:  g++ -DHAVE_CONFIG_H -I. -I.. -isystem/usr/include -W -Wall -ffor-scope -D_FILE_OFFSET_BITS=64 -D_LARGE_FILES -DMYCODESIZE=3 -MT interplm.lo -MD -MP -MF .deps/interplm.Tpo -c interplm.cpp -o interplm.o
In file included from interplm.cpp:21:
/Applications/Xcode.app/Contents/Developer/Toolchains/XcodeDefault.xctoolchain/usr/include/c++/v1/cmath:313:9: error: no member named 'signbit' in the global namespace
using ::signbit;
      ~~^
...
fatal error: too many errors emitted, stopping now [-ferror-limit=]
20 errors generated.
make[1]: *** [interplm.lo] Error 1
make: *** [install-recursive] Error 1
***() Error compiling IRSTLM. The error messages could help you 
***() in figuring what went wrong.

On Ubuntu 17.04 with GCC 6 (works fine in GCC 5):

libtool: compile:  g++ -DHAVE_CONFIG_H -I. -I.. -isystem/usr/include -W -Wall -ffor-scope -D_FILE_OFFSET_BITS=64 -D_LARGE_FILES -DMYCODESIZE=3 -MT dictionary.lo -MD -MP -MF .deps/dictionary.Tpo -c dictionary.cpp -o dictionary.o
In file included from /usr/include/c++/6/ext/string_conversions.h:41:0,
                 from /usr/include/c++/6/bits/basic_string.h:5417,
                 from /usr/include/c++/6/string:52,
                 from /usr/include/c++/6/bits/locale_classes.h:40,
                 from /usr/include/c++/6/bits/ios_base.h:41,
                 from /usr/include/c++/6/ios:42,
                 from /usr/include/c++/6/ostream:38,
                 from /usr/include/c++/6/iostream:39,
                 from mfstream.h:26,
                 from dictionary.cpp:23:
/usr/include/c++/6/cstdlib:75:25: fatal error: stdlib.h: No such file or directory
 #include_next <stdlib.h>

Both are resolved through https://github.com/kaldi-asr/kaldi/issues/1588 and https://github.com/kaldi-asr/kaldi/pull/1713, whose files this PR imports.

(In general, we should be tracking the (largely-unmaintained) IRSTLM project on GitHub anyways, as opposed to SourceForge subversion).

srvk / eesen

Import IRSTLM patching script from Kaldi #160