[freetype2] Add -fno-define-target-os-macros

Bug: 321109569
Change-Id: I1f085def18f2ea1a45244dd5a403548b441b4740
Reviewed-on: https://fuchsia-review.googlesource.com/c/third_party/freetype2/+/981496
Reviewed-by: Daniel Thornburgh <dthorn@google.com>

BUILD.gn

diff --git a/BUILD.gn b/BUILD.gn
index 297af76..81a91bd 100644
--- a/BUILD.gn
+++ b/BUILD.gn
@@ -50,7 +50,12 @@
   # Without `-fPIC`, we get the error:
   # > ld.lld: error: can't create dynamic relocation R_X86_64_64 against local symbol in readonly
   # > segment
-  cflags = [ "-fPIC" ]
+  cflags = [
+    "-fPIC",
+
+    # TODO(https://fxbug.dev/321109569): Remove once the build issue in freetype2's copy of zlib is resolved.
+    "-fno-define-target-os-macros",
+  ]
 }
 
 #TODO(mikejurka): Remove once we've migrated to the freetype2 target everywhere