<rdar://problem/6940611> libLTO.dylib needs to let linker specify path to assembler

Add lto_codegen_set_assembler_path() API which allows the linker to specify the
path to the assembler tool to run.  When assembler is used (instead of compiler)
different command line options are used.
Add LTO_API_VERSION #define so clients (linkers) can conditionalize use of new APIs.


git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@72823 91177308-0d34-0410-b5e6-96231b3b80d8

include/llvm-c/lto.h

@@ -19,6 +19,8 @@
 #include <stdbool.h>
 #include <stddef.h>
 
+#define LTO_API_VERSION 3
+
 typedef enum {
     LTO_SYMBOL_ALIGNMENT_MASK         = 0x0000001F,    /* log2 of alignment */
     LTO_SYMBOL_PERMISSIONS_MASK       = 0x000000E0,    
@@ -207,6 +209,14 @@ extern void
 lto_codegen_set_gcc_path(lto_code_gen_t cg, const char* path);
 
 
+/**
+ * Sets the location of the assembler tool to run. If not set, libLTO
+ * will use gcc to invoke the assembler.
+ */
+extern void
+lto_codegen_set_assembler_path(lto_code_gen_t cg, const char* path);
+
+
 /**
  * Adds to a list of all global symbols that must exist in the final
  * generated code.  If a function is not listed, it might be