fix(wasm-eh): native-EH link flags for the GAL WebGL test app

The native-EH migration left tests/gal-regression/wasm/Makefile on the old
Emscripten JS-exception model (-sNO_DISABLE_EXCEPTION_CATCHING, no
-fwasm-exceptions). The wxWidgets libs it links are now built with
-fwasm-exceptions, so wasm-ld couldn't resolve __cpp_exception / __c_longjmp and
the "Build GAL WebGL test app" CI step failed. This was masked until now because
the host post-process (finalize) bug killed every run before this step ran.

Compile and link with DEPS_EH_FLAGS (-fwasm-exceptions -sSUPPORT_LONGJMP=wasm
-sWASM_LEGACY_EXCEPTIONS=1), honoring the value build-gal-webgl-test.sh exports
via env.sh with a Makefile ?= fallback — matching the wxWidgets test-app build.
Drop the now-incompatible -sNO_DISABLE_EXCEPTION_CATCHING.

Verified locally: ./scripts/build-gal-webgl-test.sh links clean against the
native-EH wx libs and produces gal_webgl_test.{js,wasm}.

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

tests/gal-regression/wasm/Makefile

@@ -57,14 +57,21 @@ else
     DEBUG_LDFLAGS =
 endif
 
+# Native WebAssembly exceptions. The wxWidgets libs (and KiCad) are built with
+# -fwasm-exceptions (scripts/common/env.sh DEPS_EH_FLAGS), so this test must compile AND
+# link the same way, or wasm-ld can't resolve __cpp_exception / __c_longjmp from the wx
+# archives. ?= honors the value build-gal-webgl-test.sh exports via env.sh; the fallback
+# keeps a bare `make` working.
+DEPS_EH_FLAGS ?= -fwasm-exceptions -sSUPPORT_LONGJMP=wasm -sWASM_LEGACY_EXCEPTIONS=1
+
 # -MMD -MP generates .d dependency files for header tracking
 # This ensures header changes trigger rebuilds (prevents stale object issues)
-CXXFLAGS = $(OPT_FLAGS) $(WX_CXXFLAGS) $(KICAD_INCLUDES) -std=c++20 -MMD -MP
+CXXFLAGS = $(OPT_FLAGS) $(DEPS_EH_FLAGS) $(WX_CXXFLAGS) $(KICAD_INCLUDES) -std=c++20 -MMD -MP
 
 # Emscripten flags
-BASE_LDFLAGS = -sALLOW_MEMORY_GROWTH=1 \
+BASE_LDFLAGS = $(DEPS_EH_FLAGS) \
+               -sALLOW_MEMORY_GROWTH=1 \
                -sERROR_ON_UNDEFINED_SYMBOLS=0 \
-               -sNO_DISABLE_EXCEPTION_CATCHING \
                -sEXPORTED_FUNCTIONS=['_main','_runScenario','_getTotalScenarios','_getCurrentScenario','_getCanvasWidth','_getCanvasHeight'] \
                -sEXPORTED_RUNTIME_METHODS=['ccall','cwrap','HEAPU8'] \
                -sMODULARIZE=1 \