[flang] Modify lto testcase for AIX (#74496)

Change the lto-flags test case to check for `-bdbg:thinlto` on AIX

---------

Co-authored-by: Mark Danial <[email protected]>

Author: madanial0

flang/test/Driver/lto-flags.f90

@@ -11,9 +11,12 @@
 
 ! Also check linker plugin opt for Thin LTO
 ! RUN: %flang -### -flto=thin %s 2>&1 | FileCheck %s \
-! RUN:        --check-prefixes=%if system-darwin %{THIN-LTO-ALL%} \
+! RUN:        --check-prefixes=%if system-darwin || system-aix %{THIN-LTO-ALL%} \
 ! RUN:        %else %{THIN-LTO-ALL,THIN-LTO-LINKER-PLUGIN%}
 
+! RUN: %flang -### -flto=thin --target=powerpc64-aix %s 2>&1 | FileCheck %s \
+! RUN:        --check-prefix THIN-LTO-LINKER-AIX
+
 ! RUN: not %flang -### -S -flto=somelto %s 2>&1 | FileCheck %s --check-prefix=ERROR
 
 ! FC1 tests. Check that it does not crash.
@@ -31,5 +34,6 @@
 ! THIN-LTO-ALL: "-fc1"
 ! THIN-LTO-ALL-SAME: "-flto=thin"
 ! THIN-LTO-LINKER-PLUGIN: "-plugin-opt=thinlto"
+! THIN-LTO-LINKER-AIX: "-bdbg:thinlto"
 
 ! ERROR: error: unsupported argument 'somelto' to option '-flto=