Reword diagnostic for style; NFC

Clang diagnostics do not start with a capital letter.

Author: AaronBallman

clang/include/clang/Basic/DiagnosticDriverKinds.td

@@ -135,7 +135,7 @@ def err_drv_invalid_unwindlib_name : Error<
 def err_drv_incompatible_unwindlib : Error<
   "--rtlib=libgcc requires --unwindlib=libgcc">;
 def err_drv_incompatible_options : Error<
-  "The combination of '%0' and '%1' is incompatible">;
+  "the combination of '%0' and '%1' is incompatible">;
 def err_drv_invalid_stdlib_name : Error<
   "invalid library name in argument '%0'">;
 def err_drv_invalid_output_with_multiple_archs : Error<

clang/test/Driver/openmp-offload-jit.c

@@ -46,9 +46,9 @@
 // RUN: %clang -### --target=x86_64-unknown-linux-gnu -fopenmp=libomp -fno-offload-lto \
 // RUN:   -fopenmp-targets=nvptx64-nvidia-cuda -fopenmp-target-jit %s 2>&1 \
 // RUN: | FileCheck -check-prefix=NO-LTO %s
-// NO-LTO: error: The combination of '-fno-offload-lto' and '-fopenmp-target-jit' is incompatible
+// NO-LTO: error: the combination of '-fno-offload-lto' and '-fopenmp-target-jit' is incompatible
 
 // RUN: %clang -### --target=x86_64-unknown-linux-gnu -fopenmp=libomp -foffload-lto=thin \
 // RUN:   -fopenmp-targets=nvptx64-nvidia-cuda -fopenmp-target-jit %s 2>&1 \
 // RUN: | FileCheck -check-prefix=THIN-LTO %s
-// THIN-LTO: error: The combination of '-foffload-lto=' and '-fopenmp-target-jit' is incompatible
+// THIN-LTO: error: the combination of '-foffload-lto=' and '-fopenmp-target-jit' is incompatible