build: Add a comment to libbsd-overlay.pc about -isystem usage

Add the reasoning for why we use -isystem instead of -I, to avoid
confusing unsuspecting readers of the file.

Prompted-by: Alejandro Colomar <alx@kernel.org>

diff --git a/src/libbsd-overlay.pc.in b/src/libbsd-overlay.pc.in
index 0455f224fade320cfb39112a60bdc6e910fe3cc8..7ef4e4d56684baa9374f12cfee1292f25cba4718 100644 (file)
--- a/src/libbsd-overlay.pc.in
+++ b/src/libbsd-overlay.pc.in
@@ -9,4 +9,5 @@ Version: @VERSION@
 URL: https://libbsd.freedesktop.org/
 Libs: -L${libdir} -lbsd
 Libs.private: @LIBBSD_LIBS@ @MD5_LIBS@
+# We use -isystem instead of -I due the overlay via #include_next usage.
 Cflags: -isystem ${includedir}/bsd -DLIBBSD_OVERLAY