[AIX] Add a dummy variable in the __llvm_orderfile section (#81968)

to satisfy the __start___llvm_orderfile reference when linking with
-bexpfull and -fprofile-generate on AIX.

(cherry picked from commit 15cccc55919d27eb2e89379a65f6c7809f679fda)

compiler-rt/lib/profile/InstrProfilingPlatformAIX.c

@@ -195,6 +195,8 @@ static const int dummy_name[0] COMPILER_RT_SECTION(
     COMPILER_RT_SEG INSTR_PROF_NAME_SECT_NAME);
 static int dummy_vnds[0] COMPILER_RT_SECTION(
     COMPILER_RT_SEG INSTR_PROF_VNODES_SECT_NAME);
+static int dummy_orderfile[0] COMPILER_RT_SECTION(
+    COMPILER_RT_SEG INSTR_PROF_ORDERFILE_SECT_NAME);
 
 // To avoid GC'ing of the dummy variables by the linker, reference them in an
 // array and reference the array in the runtime registration code
@@ -206,7 +208,7 @@ static int dummy_vnds[0] COMPILER_RT_SECTION(
 COMPILER_RT_VISIBILITY
 void *__llvm_profile_keep[] = {(void *)&dummy_cnts, (void *)&dummy_bits,
                                (void *)&dummy_data, (void *)&dummy_name,
-                               (void *)&dummy_vnds};
+                               (void *)&dummy_vnds, (void *)&dummy_orderfile};
 #ifdef __GNUC__
 #pragma GCC diagnostic pop
 #endif

compiler-rt/test/profile/AIX/bexpfull-pgo.c

@@ -0,0 +1,7 @@
+// RUN: %clang_pgogen %s -bexpall
+// RUN: %clang_pgogen %s -bexpfull
+
+#include <string.h>
+int ar[10];
+int n;
+int main() { memcpy(ar, ar + 1, n); };