[Instrumented libraries] Fix font loading issues

* FontConfig's FC_PATH is returned relative to the sysroot [1], so the
  sysroot must be prepended when resolving the real path.
* There's a likely a bug in the MSAN runtime where variables passed to
  variadic C functions with a large number of arguments incorrectly get
  reported as uninitialized memory.  This CL adds a workaround that
  removes a variadic function in Pango.
* Also remove goma.gni as it no longer exists.

[1] https://www.freedesktop.org/software/fontconfig/fontconfig-devel/x19.html

Bug: 333609800
Change-Id: I19cd9ba7c32c98fb744ec9810db29ef2e0127253
R=thestig
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/third_party/instrumented_libraries/+/5551798
Reviewed-by: Lei Zhang <thestig@chromium.org>
3 files changed