cmake: Inline the add_llvm_symbol_exports.py script

This fixes stand-alone builds.

Reviewed By: andrewng

Differential Revision: https://reviews.llvm.org/D137611

Author: tstellar

llvm/cmake/modules/AddLLVM.cmake

@@ -103,7 +103,13 @@ function(add_llvm_symbol_exports target_name export_file)
     # FIXME: Don't write the "local:" line on OpenBSD.
     # in the export file, also add a linker script to version LLVM symbols (form: LLVM_N.M)
     add_custom_command(OUTPUT ${native_export_file}
-      COMMAND "${Python3_EXECUTABLE}" ${LLVM_MAIN_SRC_DIR}/utils/add_llvm_symbol_exports.py ${LLVM_VERSION_MAJOR} ${export_file} ${native_export_file}
+      COMMAND "${Python3_EXECUTABLE}" "-c"
+      "import sys; \
+       lines = ['    ' + l.rstrip() for l in sys.stdin] + ['  local: *;']; \
+       print('LLVM_${LLVM_VERSION_MAJOR} {'); \
+       print('  global:') if len(lines) > 1 else None; \
+       print(';\\n'.join(lines) + '\\n};')"
+      < ${export_file} > ${native_export_file}
       DEPENDS ${export_file}
       VERBATIM
       COMMENT "Creating export file for ${target_name}")