BUILD: makefile: add new option USE_MEMORY_PROFILING

It is not enabled by default, and may only work on linux-glibc for now,
though maybe other platforms could adopt it, possibly with certain
restrictions.
diff --git a/Makefile b/Makefile
index 46ae734..2d0b7d8 100644
--- a/Makefile
+++ b/Makefile
@@ -55,6 +55,7 @@
 #   USE_OBSOLETE_LINKER  : use when the linker fails to emit __start_init/__stop_init
 #   USE_THREAD_DUMP      : use the more advanced thread state dump system. Automatic.
 #   USE_OT               : enable the OpenTracing filter
+#   USE_MEMORY_PROFILING : enable the memory profiler. Linux-glibc only.
 #
 # Options can be forced by specifying "USE_xxx=1" or can be disabled by using
 # "USE_xxx=" (empty string). The list of enabled and disabled options for a
@@ -309,7 +310,7 @@
            USE_CLOSEFROM USE_ZLIB USE_SLZ USE_CPU_AFFINITY USE_TFO USE_NS     \
            USE_DL USE_RT USE_DEVICEATLAS USE_51DEGREES USE_WURFL USE_SYSTEMD  \
            USE_OBSOLETE_LINKER USE_PRCTL USE_THREAD_DUMP USE_EVPORTS USE_OT   \
-           USE_QUIC USE_PROMEX
+           USE_QUIC USE_PROMEX USE_MEMORY_PROFILING
 
 #### Target system options
 # Depending on the target platform, some options are set, as well as some