[clang][driver] Improve warning message for target AVR (llvm#114394)

Fixes llvm#96743

Author: benshi001

clang/include/clang/Basic/DiagnosticDriverKinds.td

@@ -37,8 +37,7 @@ def warn_drv_invalid_arch_name_with_suggestion : Warning<
   "ignoring invalid /arch: argument '%0'; for %select{64|32}1-bit expected one of %2">,
   InGroup<UnusedCommandLineArgument>;
 def warn_drv_avr_mcu_not_specified : Warning<
-  "no target microcontroller specified on command line, cannot "
-  "link standard libraries, please pass -mmcu=<mcu name>">,
+  "no target microcontroller specified, please pass -mmcu=<mcu name>">,
   InGroup<AVRRtlibLinkingQuirks>;
 def warn_drv_avr_libc_not_found: Warning<
   "no avr-libc installation can be found on the system, "

clang/test/Driver/avr-toolchain.c

@@ -44,7 +44,7 @@
 // RUN: %clang -### --target=avr --sysroot=%S/Inputs/basic_avr_tree -S %s 2>&1 | FileCheck --check-prefixes=NOMCU,LINKA %s
 // RUN: %clang -### --target=avr --sysroot=%S/Inputs/ -S %s 2>&1 | FileCheck --check-prefixes=NOMCU,LINKA %s
 // RUN: %clang -### --target=avr --sysroot=%S/Inputs/basic_avr_tree %s 2>&1 | FileCheck --check-prefixes=NOMCU,LINKB %s
-// NOMCU: warning: no target microcontroller specified on command line, cannot link standard libraries, please pass -mmcu=<mcu name>
+// NOMCU: warning: no target microcontroller specified, please pass -mmcu=<mcu name>
 // LINKB: warning: standard library not linked and so no interrupt vector table or compiler runtime routines will be linked
 // LINKB: warning: support for passing the data section address to the linker for microcontroller '' is not implemented
 // NOMCU-NOT: warning: {{.*}} avr-gcc