Fix additional issues reported by UB sanitizers

Most of these involved overrunning the signed 32-bit JLONG type whenever
building libjpeg-turbo with a 32-bit compiler.  These issues are not
believed to represent actual security threats, but eliminating them
makes it easier to detect such threats should they arise in the future.
diff --git a/ChangeLog.txt b/ChangeLog.txt
index 4a6f488..a064973 100644
--- a/ChangeLog.txt
+++ b/ChangeLog.txt
@@ -29,6 +29,12 @@
 [6] The MIPS DSPr2 SIMD code can now be compiled to support either FR=0 or FR=1
 FPUs.
 
+[7] Fixed additional negative left shifts and other issues reported by the GCC
+and Clang undefined behavior sanitizers.  Most of these issues affected only
+32-bit code, and none of them was known to pose a security threat, but removing
+the warnings makes it easier to detect actual security issues, should they
+arise in the future.
+
 
 1.4.2
 =====