My 1.8.3 build has not completed. HOWEVER, I can already see a key difference in the configure step.
In 1.8.3 "-mt" was added AUTOMATICALLY to CFLAGS by configure: checking if C compiler and POSIX threads work as is... no - Solaris, not checked checking if C++ compiler and POSIX threads work as is... no - Solaris, not checked checking if Fortran compiler and POSIX threads work as is... no - Solaris, not checked checking if C compiler and POSIX threads work with -pthread... no checking if C compiler and POSIX threads work with -pthreads... no checking if C compiler and POSIX threads work with -mt... yes checking if C++ compiler and POSIX threads work with -pthread... yes checking if Fortran compiler and POSIX threads work with -pthread... yes This is not the case in 1.8.4rc4: checking if C compiler and POSIX threads work as is... yes checking if C++ compiler and POSIX threads work as is... yes checking if Fortran compiler and POSIX threads work as is... yes So, it looks like a chunk of Solaris-specific configure logic was LOST. -Paul