build: meson support for libphosphor-logging

Create just enough meson directives to create the equivalent
of libphosphor-logging, so that this repository can be picked
up as a meson subproject.  Remainder of the conversion to meson
will be in follow-on commits.

Signed-off-by: Patrick Williams <patrick@stwcx.xyz>
Change-Id: Ifbcc58b118352d8f0338221c4cb7e472c2be7a43
diff --git a/.gitignore b/.gitignore
index 10293c4..628fd48 100644
--- a/.gitignore
+++ b/.gitignore
@@ -1,3 +1,7 @@
+build*/
+subprojects/*
+!subprojects/*.wrap
+
 Makefile
 Makefile.in
 aclocal.m4