add escapes to preserve string argument

Signed-off-by: Kimball Thurston <kdt3rd@gmail.com>

Author: kdt3rd

.github/workflows/ci_steps.yml

@@ -155,8 +155,8 @@ jobs:
           fi
           if [ "${{ inputs.msystem }}" == "MINGW32" ]; then
               CMAKE_ARGS="$CMAKE_ARGS \
-                 -DCMAKE_C_FLAGS='-msse2 -mfpmath=sse' \
-                 -DCMAKE_CXX_FLAGS='-msse2 -mfpmath=sse'"
+                 -DCMAKE_C_FLAGS=\\'-msse2 -mfpmath=sse\\' \
+                 -DCMAKE_CXX_FLAGS=\\'-msse2 -mfpmath=sse\\'"
           fi
 
           echo "CMAKE_ARGS=$CMAKE_ARGS" >> $GITHUB_ENV