library: extend thread safety to more static variables

In the commit referenced below, a '__thread' attribute
was added to numerous static variables to protect them
from concurrent access conflicts with multi-threading.

Unfortunately, that patch did not go quite far enough.

So, this commit adds a few more '__thread' qualifiers.

Reference(s):
commit 23cfb71366

Signed-off-by: Jim Warner <james.warner@comcast.net>

proc/readproc.c

@@ -58,8 +58,8 @@ extern void __cyg_profile_func_enter(void*,void*);
 
 // utility buffers of MAX_BUFSZ bytes each, available to
 // any function following an openproc() call
-static char *src_buffer,
-            *dst_buffer;
+static __thread char *src_buffer,
+                     *dst_buffer;
 #define MAX_BUFSZ 1024*64*2
 
 // dynamic 'utility' buffer support for file2str() calls