Use dummy AOT reloc functions when building wamrc

AOT reloc functions are used only when loading AOT WebAssembly modules
on target, not during AOT compilation. Original code led to build issues
when building wamrc as cross-compiler, using arm header on x86 build.

Author: peter-tatrai

core/iwasm/aot/arch/aot_reloc_dummy.c

@@ -0,0 +1,41 @@
+/*
+ * Copyright (C) 2020 Intel Corporation. All rights reserved.
+ * SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
+ */
+
+#include "aot_reloc.h"
+#include <stdlib.h>
+
+SymbolMap *
+get_target_symbol_map(uint32 *sym_num)
+{
+    abort();
+}
+
+uint32
+get_plt_table_size(void)
+{
+    abort();
+}
+
+void
+init_plt_table(uint8 *plt)
+{
+    abort();
+}
+
+void
+get_current_target(char *target_buf, uint32 target_buf_size)
+{
+    abort();
+}
+
+bool
+apply_relocation(AOTModule *module,
+                 uint8 *target_section_addr, uint32 target_section_size,
+                 uint64 reloc_offset, int64 reloc_addend,
+                 uint32 reloc_type, void *symbol_addr, int32 symbol_index,
+                 char *error_buf, uint32 error_buf_size)
+{
+    abort();
+}

core/iwasm/aot/iwasm_aot.cmake

@@ -21,7 +21,10 @@ if (WAMR_BUILD_AOT_VALIDATOR EQUAL 1)
   list (APPEND c_source_all ${IWASM_AOT_DIR}/aot_validator.c)
 endif ()
 
-if (WAMR_BUILD_TARGET STREQUAL "X86_64" OR WAMR_BUILD_TARGET STREQUAL "AMD_64")
+if (WAMR_AOT_COMPILER EQUAL 1)
+  # AOT reloc functions are not used during AOT compilation
+  set (arch_source ${IWASM_AOT_DIR}/arch/aot_reloc_dummy.c)
+elseif (WAMR_BUILD_TARGET STREQUAL "X86_64" OR WAMR_BUILD_TARGET STREQUAL "AMD_64")
   set (arch_source ${IWASM_AOT_DIR}/arch/aot_reloc_x86_64.c)
 elseif (WAMR_BUILD_TARGET STREQUAL "X86_32")
   set (arch_source ${IWASM_AOT_DIR}/arch/aot_reloc_x86_32.c)

wamr-compiler/CMakeLists.txt

@@ -265,6 +265,8 @@ else ()
   message ("-- Lib wasi-threads disabled")
 endif ()
 
+set (WAMR_AOT_COMPILER 1)
+
 include (${SHARED_DIR}/platform/${WAMR_BUILD_PLATFORM}/shared_platform.cmake)
 include (${SHARED_DIR}/mem-alloc/mem_alloc.cmake)
 include (${SHARED_DIR}/utils/shared_utils.cmake)