Use PKG_CONFIG_LIBDIR to force pkg-config to use sysroot only

build/linux/pkg-config-wrapper

Index: build/linux/pkg-config-wrapper
diff --git a/build/linux/pkg-config-wrapper b/build/linux/pkg-config-wrapper
index 2afb22ba7c5ed0aa3c952b106887f6fc002d2566..2512b38837394e235eacd0edbf99cbcbdb6d8c20 100755
--- a/build/linux/pkg-config-wrapper
+++ b/build/linux/pkg-config-wrapper
@@ -15,6 +15,9 @@
 # the PKG_CONFIG_PATH environment variable- these will be prepended to the
 # generated paths.
 
+set -o nounset
+set -o errexit
+
 root="$1"
 shift
 target_arch="$1"
@@ -31,13 +34,7 @@ fi
 rewrite=`dirname $0`/rewrite_dirs.py
 package=${!#}
 
-config_path=$root/usr/$libpath/pkgconfig:$root/usr/share/pkgconfig
-
-# prepend any paths specified by the environment
-if [ -n "$PKG_CONFIG_PATH" ]
-then
-  config_path="$PKG_CONFIG_PATH:$config_path"
-fi
+libdir=$root/usr/$libpath/pkgconfig:$root/usr/share/pkgconfig
 
 set -e
 # Some sysroots, like the Chromium OS ones, may generate paths that are not
@@ -47,6 +44,6 @@ set -e
 # relative to /path/to/chroot/build/x86-generic (i.e prefix=/usr).
 # To support this correctly, it's necessary to extract the prefix to strip from
 # pkg-config's |prefix| variable.
-prefix=`PKG_CONFIG_PATH=$config_path pkg-config --variable=prefix "$package" | sed -e 's|/usr$||'`
-result=`PKG_CONFIG_PATH=$config_path pkg-config "$@"`
+prefix=`PKG_CONFIG_LIBDIR=$libdir pkg-config --variable=prefix "$package" | sed -e 's|/usr$||'`
+result=`PKG_CONFIG_LIBDIR=$libdir pkg-config "$@"`
 echo "$result"| $rewrite --sysroot "$root" --strip-prefix "$prefix"