proc: shotgun test read/readdir/readlink + a little write

Interact with nearly everything in /proc.

Hopefully memleak checkers and KASAN will find something.

---

 tools/testing/selftests/proc/.gitignore |    1 
 tools/testing/selftests/proc/Makefile   |    1 
 tools/testing/selftests/proc/read.c     |  146 ++++++++++++++++++++++++++++++++
 3 files changed, 148 insertions(+)

@@ -4,3 +4,4 @@
 /proc-self-map-files-002
 /proc-self-syscall
 /proc-self-wchan
+/read

@@ -7,5 +7,6 @@ TEST_GEN_PROGS += proc-self-map-files-001
 TEST_GEN_PROGS += proc-self-map-files-002
 TEST_GEN_PROGS += proc-self-syscall
 TEST_GEN_PROGS += proc-self-wchan
+TEST_GEN_PROGS += read
 
 include ../lib.mk

new file mode 100644