[LLDB][PDB] Fix plugin warning message style (#160398)

Makes the warning message conform to the [LLVM error and warning
style](https://llvm.org/docs/CodingStandards.html#error-and-warning-messages)
as mentioned in
#160067 (comment).

Author: Nerixyz

lldb/source/Plugins/SymbolFile/PDB/SymbolFilePDB.cpp

@@ -139,8 +139,8 @@ class PluginProperties : public Properties {
     if (!IsNativeReaderRequested()) {
       static std::once_flag g_warning_shown;
       Debugger::ReportWarning(
-          "The DIA PDB reader was explicitly requested, but LLDB was built "
-          "without the DIA SDK. The native reader will be used instead.",
+          "the DIA PDB reader was explicitly requested, but LLDB was built "
+          "without the DIA SDK. The native reader will be used instead",
           {}, &g_warning_shown);
     }
     return true;

lldb/test/Shell/SymbolFile/NativePDB/native-setting.cpp

@@ -38,7 +38,7 @@
 // NO-ENV: Dumping debug symbols for 1 modules.
 // NO-ENV: SymbolFile native-pdb
 
-// ENV0: warning: The DIA PDB reader was explicitly requested, but LLDB was built without the DIA SDK. The native reader will be used instead.
+// ENV0: warning: the DIA PDB reader was explicitly requested, but LLDB was built without the DIA SDK. The native reader will be used instead
 // ENV0: (lldb) target modules dump symfile
 // ENV0: Dumping debug symbols for 1 modules.
 // ENV0: SymbolFile native-pdb
@@ -48,12 +48,12 @@
 // ENV1: Dumping debug symbols for 1 modules.
 // ENV1: SymbolFile native-pdb
 
-// ENV0-SET-DIA: warning: The DIA PDB reader was explicitly requested, but LLDB was built without the DIA SDK. The native reader will be used instead.
+// ENV0-SET-DIA: warning: the DIA PDB reader was explicitly requested, but LLDB was built without the DIA SDK. The native reader will be used instead
 // ENV0-SET-DIA: (lldb) target modules dump symfile
 // ENV0-SET-DIA: Dumping debug symbols for 1 modules.
 // ENV0-SET-DIA: SymbolFile native-pdb
 
-// ENV1-SET-DIA: warning: The DIA PDB reader was explicitly requested, but LLDB was built without the DIA SDK. The native reader will be used instead.
+// ENV1-SET-DIA: warning: the DIA PDB reader was explicitly requested, but LLDB was built without the DIA SDK. The native reader will be used instead
 // ENV1-SET-DIA: (lldb) target modules dump symfile
 // ENV1-SET-DIA: Dumping debug symbols for 1 modules.
 // ENV1-SET-DIA: SymbolFile native-pdb