fix: avoid warning by dropping '#pragma once'

Before this change, we would see the warning:

	"#pragma once in main file"

Author: tobiasgrosser

src/runtime/CMakeLists.txt

@@ -24,6 +24,8 @@ if(LLVM)
   FILE(READ "${CMAKE_CURRENT_SOURCE_DIR}/../include/lean/lean.h" LEAN_H)
   # generate LLVM IR for `static inline` definitions in lean.h for the LLVM backend
   string(REPLACE "static inline" "__attribute__((always_inline))" LEAN_H "${LEAN_H}")
+  # drop '#pragma once' in .c file to avoid warning
+  string(REPLACE "#pragma once" "" LEAN_H "${LEAN_H}")
   file(WRITE "${CMAKE_CURRENT_BINARY_DIR}/lean_inlines.c" "${LEAN_H}")
   message("Generating LLVM bitcode file for Lean runtime at '${CMAKE_LIBRARY_OUTPUT_DIRECTORY}/lean.h.bc'")
   add_custom_command(