clang: Makes builds with clang less dependent on absolute file path

build/config/linux/pkg_config.gni

Index: build/config/linux/pkg_config.gni
diff --git a/build/config/linux/pkg_config.gni b/build/config/linux/pkg_config.gni
index 914ca8d6e728ae8eb3826e760246c6561fe28df6..e81d527ec40b0f324a75f4b863c80cd9ee7c2b55 100644
--- a/build/config/linux/pkg_config.gni
+++ b/build/config/linux/pkg_config.gni
@@ -41,7 +41,7 @@ if (sysroot != "") {
   # Pass the sysroot if we're using one (it requires the CPU arch also).
   pkg_config_args = [
     "-s",
-    sysroot,
+    rebase_path(sysroot, "", ".."),

[brettw, 2016/01/06 18:15:07]

Wait, I don't understand this line. Why the ".."?

[Zachary Forman, 2016/01/06 23:20:49]

Without the .., you get output like
"-I../../build/build/linux/debian_wheezy_amd64-sysroot/usr/include/glib-2.0" -
note the "build/build".

[brettw, 2016/01/07 19:22:22]

Semantically I don't think this line makes sense, and if it's working for you I
suspect it's a coincidence.

Sysroot is an absolute path. This line says "take the absolute path and make it
relative to the current directory ("build/config/linux") assuming that the
source is in the the previous directory ("build/config")."

What directory are you specifically trying to pass to the -s command, and where
should it be expressed relative to?

[Zachary Forman, 2016/01/07 22:54:27]

I don't think this is the case. To start with,the point of this change is that
we're making sysroots relative paths, and this change converts a relative path
sysroot from the output directory to the correct absolute path.

print("sysroot        = $sysroot")
print("rebased        = " + rebase_path(sysroot, "", ".."))
print("rebased w/o .. = " + rebase_path(sysroot, "", ".."))
->
sysroot        = ../../build/linux/debian_wheezy_amd64-sysroot
rebased        =
/usr/local/google/home/zforman/chromium-1/src/build/linux/debian_wheezy_amd64-sysroot
rebased w/o .. =
/usr/local/google/home/zforman/chromium-1/src/build/build/linux/debian_wheezy_amd64-sysroot

What this is doing is then taking ../../build/... and rebasing it to an absolute
path from.

This file is located in build/config/linux/ - therefore we absolutify
(build/config/linux/../)(../../build/linux/debian_wheezy_amd64-sysroot) ->
build/linux/debian_wheezy_amd64-sysroot.

     "-a",
     current_cpu,
   ]