liblzma: Disable XL compiler optimizations altogether

Revert commit 82c51a8a (liblzma: Disable XL compiler optimizations in
one source to avoid crash, 2015-04-02) and instead add a compiler flag
to disable optimizations in every source of liblzma.  Somehow the XL
compiler optimizations create incorrect behavior in liblzma and lead
to crashes or truncated output during compression.

Utilities/cmliblzma/CMakeLists.txt

@@ -211,4 +211,10 @@ ENDIF()
 
 ADD_LIBRARY(cmliblzma ${LZMA_SRCS})
 
+IF(CMAKE_C_COMPILER_ID STREQUAL "XL")
+  # Disable the XL compiler optimizer because it causes crashes
+  # and other bad behavior in liblzma code.
+  SET_PROPERTY(TARGET cmliblzma PROPERTY COMPILE_FLAGS "-qnooptimize")
+ENDIF()
+
 INSTALL(FILES COPYING DESTINATION ${CMAKE_DOC_DIR}/cmliblzma)

Utilities/cmliblzma/liblzma/lzma/lzma_encoder_optimum_normal.c

@@ -8,9 +8,6 @@
 //  You can do whatever you want with this file.
 //
 ///////////////////////////////////////////////////////////////////////////////
-#if defined(__IBMC__)
-# pragma options optimize=0
-#endif
 
 #include "lzma_encoder_private.h"
 #include "fastpos.h"