+# -DNO_PROC_STAT Causes the collector to avoid relying on Linux'
+# /proc/self/stat.
+# -DNO_GETCONTEXT Causes the collector to not assume the existence of
+# the getcontext() function on linux-like platforms. This currently
+# happens implicitly on Darwin, Hurd, or ARM or MIPS hardware.
+# It is explicitly needed for some old versions of FreeBSD.
+# -DSTATIC=static Causes various GC_ symbols that could logically be
+# declared static to be declared (this is the default if -DNO_DEBUGGING is
+# specified). Reduces the number of visible symbols (letting the optimizer
+# do its work better), which is probably cleaner, but may make some kinds of
+# debugging and profiling harder.
+# -DDONT_USE_USER32_DLL (Win32 only) Don't use "user32" DLL import library
+# (containing MessageBox() entry); useful for a static GC library.
+# -DGC_PREFER_MPROTECT_VDB Choose MPROTECT_VDB manually in case of multiple
+# virtual dirty bit strategies are implemented (at present useful on Win32
+# to force MPROTECT_VDB strategy instead of the default GWW_VDB one).