Some libraries (jpeg, xpcom) include nsprpub header files and need to know about USE_PTHREADS for some platforms (SparcLinux/RH5.1).

config/config.mk

@@ -673,3 +673,9 @@ JAVA_DEFINES    += -DAWT_11
 else
 JAVA_DEFINES    += -DAWT_102
 endif
+
+# From nsprpub/config/config.mk, mozilla/jpeg needs to know
+# about USE_PTHREADS.  This fixes platforms like SparcLinux. -mcafee
+ifeq ($(USE_PTHREADS), 1)
+OS_CFLAGS += -D_PR_PTHREADS -UHAVE_CVAR_BUILT_ON_SEM
+endif