Fix support for GNU/kFreeBSD

The configure.ac seciton right now is the same for Linux and kFreeBSD,
which results into an incorrect configuration of e.g. defining
JEMALLOC_PROC_SYS_VM_OVERCOMMIT_MEMORY instead of FreeBSD's
JEMALLOC_SYSCTL_VM_OVERCOMMIT.

GNU/kFreeBSD is really a glibc + FreeBSD kernel system, so it needs its
own entry which has a mixture of configuration options from Linux and
FreeBSD.

configure.ac

@@ -567,7 +567,7 @@ case "${host}" in
 	  default_retain="1"
 	fi
 	;;
-  *-*-linux* | *-*-kfreebsd*)
+  *-*-linux*)
 	dnl syscall(2) and secure_getenv(3) are exposed by _GNU_SOURCE.
 	JE_APPEND_VS(CPPFLAGS, -D_GNU_SOURCE)
 	abi="elf"
@@ -580,6 +580,15 @@ case "${host}" in
 	  default_retain="1"
 	fi
 	;;
+  *-*-kfreebsd*)
+	dnl syscall(2) and secure_getenv(3) are exposed by _GNU_SOURCE.
+	JE_APPEND_VS(CPPFLAGS, -D_GNU_SOURCE)
+	abi="elf"
+	AC_DEFINE([JEMALLOC_HAS_ALLOCA_H])
+	AC_DEFINE([JEMALLOC_SYSCTL_VM_OVERCOMMIT], [ ])
+	AC_DEFINE([JEMALLOC_THREADED_INIT], [ ])
+	AC_DEFINE([JEMALLOC_USE_CXX_THROW], [ ])
+	;;
   *-*-netbsd*)
 	AC_MSG_CHECKING([ABI])
         AC_COMPILE_IFELSE([AC_LANG_PROGRAM(