Include the library directory for the sake of 3rdparty

When compiling library files under `3rdparty/`, the directory containing
the `.c` file that is being compiled is not the current directory, so
headers from the `library/` directory are not found. Fix this by
adding `.` to the include path.

This was not detected until now because as of this commit, no 3rdparty
source file requires a header under `library/`.

Signed-off-by: Gilles Peskine <Gilles.Peskine@arm.com>
diff --git a/library/Makefile b/library/Makefile
index dbdd3b6..801304b 100644
--- a/library/Makefile
+++ b/library/Makefile
@@ -5,7 +5,7 @@
 WARNING_CFLAGS ?=  -Wall -Wextra
 LDFLAGS ?=
 
-LOCAL_CFLAGS = $(WARNING_CFLAGS) -I../include -D_FILE_OFFSET_BITS=64
+LOCAL_CFLAGS = $(WARNING_CFLAGS) -I. -I../include -D_FILE_OFFSET_BITS=64
 LOCAL_LDFLAGS =
 
 ifdef DEBUG