Turn off PartitionAlloc when building with GCC as well.

As GCC 12 on Linux cannot build PartitionAlloc either, change the
pdf_use_partition_alloc_override logic to just check if the compiler is
Clang.

Change-Id: I2e3cacb59d1618e9b2d788ed6b5d558a2d00671c
Reviewed-on: https://pdfium-review.googlesource.com/c/pdfium/+/100670
Reviewed-by: Tom Sepez <tsepez@chromium.org>
Commit-Queue: Lei Zhang <thestig@chromium.org>
diff --git a/build_overrides/pdfium.gni b/build_overrides/pdfium.gni
index 71051da..f16ac0b 100644
--- a/build_overrides/pdfium.gni
+++ b/build_overrides/pdfium.gni
@@ -19,8 +19,8 @@
 
 # Build PDFium with PartitionAlloc support, directing `fxcrt` to use
 # it as its memory allocator in lieu of `malloc()`.
-# Default: Use PartitionAlloc unless it is a MSVC build.
-pdf_use_partition_alloc_override = !is_win || is_clang
+# Default: Use PartitionAlloc when building with Clang.
+pdf_use_partition_alloc_override = is_clang
 
 # Build PDFium to use Skia (experimental) for all PDFium graphics.
 # If enabled, coexists in build with AGG graphics and the default