pkgconf: don't double prefix lib/include paths with sysroot

A .pc file could contain statements of the form:
    -L/usr/lib
but also:
    -L/path/to/sysroot/usr/lib

The latter form typically occurs when the dependency was configured with a
statement like --with-xxx=$(STAGING_DIR)/usr.

pkgconf only expects the first form, and prefixes it with the specified
sysroot. However, this strategy would result in a double sysroot in the
second case:
    -L/path/to/sysroot/path/to/sysroot/usr/lib

This patch checks for the presence of the sysroot in the specified -L or -I
directives, and only adds the sysroot when not already present.

Upstream-status: will be submitted

Signed-off-by: Thomas De Schampheleire <thomas.de.schampheleire@gmail.com>

---
 main.c |  3 ++-
 1 files changed, 2 insertions(+), 1 deletions(-)


diff -r 16865d81819f -r 9d8e1737687f main.c
--- a/main.c	Mon Jun 16 19:47:52 2014 +0200
+++ b/main.c	Mon Jun 16 19:48:15 2014 +0200
@@ -82,7 +82,8 @@
 	{
 	case 'L':
 	case 'I':
-		return sysroot_dir;
+		if (strncmp(sysroot_dir, frag->data, strlen(sysroot_dir)) != 0)
+			return sysroot_dir;
 	default:
 		break;
 	}