fix(cmake): add required emscripten flags (#5298)

* fix(cmake): add required emscripten flags

Signed-off-by: Henry Schreiner <henryschreineriii@gmail.com>

* Update emscripten.yaml

* fix(cmake): add required emscripten flags to headers target

Signed-off-by: Henry Schreiner <henryschreineriii@gmail.com>

* fix(cmake): incorrect detection of Emscripten

Signed-off-by: Henry Schreiner <henryschreineriii@gmail.com>

* fix(cmake): allow pybind11::headers to be modified

Signed-off-by: Henry Schreiner <henryschreineriii@gmail.com>

* fix(cmake): hide a warning when building the tests standalone

Signed-off-by: Henry Schreiner <henryschreineriii@gmail.com>

* fix(cmake): use explicit variable for is config

Signed-off-by: Henry Schreiner <henryschreineriii@gmail.com>

* fix(cmake): go back to ALIAS target

Signed-off-by: Henry Schreiner <henryschreineriii@gmail.com>

* chore: reduce overall diff

Signed-off-by: Henry Schreiner <henryschreineriii@gmail.com>

* chore: reduce overall diff

Signed-off-by: Henry Schreiner <henryschreineriii@gmail.com>

* chore: shorten code a bit

Signed-off-by: Henry Schreiner <henryschreineriii@gmail.com>

---------

Signed-off-by: Henry Schreiner <henryschreineriii@gmail.com>

.github/workflows/emscripten.yaml

@@ -5,6 +5,8 @@ on:
   pull_request:
     branches:
     - master
+    - stable
+    - v*
 
 concurrency:
   group: ${{ github.workflow }}-${{ github.ref }}
@@ -23,8 +25,6 @@ jobs:
     - uses: pypa/cibuildwheel@v2.20
       env:
         PYODIDE_BUILD_EXPORTS: whole_archive
-        CFLAGS: -fexceptions
-        LDFLAGS: -fexceptions
       with:
         package-dir: tests
         only: cp312-pyodide_wasm32