fix(build): download baseline WebKit for x64 baseline builds

When ENABLE_BASELINE=ON is set for x86_64 builds, append `-baseline`
to the WebKit download URL suffix. Without this, baseline Bun links
against a WebKit library compiled with AVX/AVX2 instructions, causing
SIGILL crashes on CPUs without AVX support.

The baseline suffix is placed after the musl suffix and before the
debug/lto/asan suffixes to match the naming convention used by the
WebKit CI (oven-sh/WebKit#137).

Closes #27090

Co-Authored-By: Claude <noreply@anthropic.com>

cmake/tools/SetupWebKit.cmake

@@ -209,6 +209,10 @@ if(LINUX AND ABI STREQUAL "musl")
   set(WEBKIT_SUFFIX "-musl")
 endif()
 
+if(ENABLE_BASELINE AND WEBKIT_ARCH STREQUAL "amd64")
+  set(WEBKIT_SUFFIX "${WEBKIT_SUFFIX}-baseline")
+endif()
+
 if(DEBUG)
   set(WEBKIT_SUFFIX "${WEBKIT_SUFFIX}-debug")
 elseif(ENABLE_LTO)