Add comment explaining why both CMAKE_ARGS and ENV compiler variables are needed

CMAKE_ARGS configures CMake with the correct compilers, while ENV variables
ensure build tools and subprocesses use the right compilers, which is
important for complex builds like Hermes.

Author: JoaoPauloCMarra

cmake/HermesExternal.cmake

@@ -92,6 +92,10 @@ else()
     )
 
     # Add Hermes as external project
+    # Note: Both CMAKE_ARGS and ENV variables are used to ensure compiler consistency.
+    # CMAKE_ARGS tells CMake which compilers to configure with, while ENV variables
+    # ensure that build tools (make/ninja) and subprocesses use the correct compilers,
+    # which is important for complex builds like Hermes that may spawn additional processes.
     ExternalProject_Add(hermes
         GIT_REPOSITORY ${HERMES_GIT_URL}
         GIT_TAG ${HERMES_GIT_TAG}