Add probabability distribution utility code.

Add probabability distribution utility code that enables generation of
random deviates drawn from normal, Chi-square, and Gamma distributions.

Fix format strings in several of the assert_* macros (remove a %s).

Clean up header issues; it's critical that system headers are not
included after internal definitions potentially do things like:

  #define inline

Fix the build system to incorporate header dependencies for the test
library C files.

include/jemalloc/internal/jemalloc_internal_macros.h

@@ -37,6 +37,7 @@
 
 #define	ZU(z)	((size_t)z)
 #define	QU(q)	((uint64_t)q)
+#define	QI(q)	((int64_t)q)
 
 #ifndef __DECONST
 #  define	__DECONST(type, var)	((type)(uintptr_t)(const void *)(var))