Core/Common: Add a generic config helper to access built-in overwriteable paths.

* Adds CMAKE_COMMAND and CMAKE_BINARY_DIR to revision_data.h
* Move the source and mysql exe path handling out of the DBUpdater.
* Make some Config methods const for correctness.
* Remove C & CXX flags from revision_data.h
 (was unused and didn't capture all cxx vars)
* Reorder the link order to prevent `ld` from ignoring the file
* Ref #15671

src/common/GitRevision.cpp

@@ -17,6 +17,16 @@ char const* GitRevision::GetBranch()
     return _BRANCH;
 }
 
+char const* GitRevision::GetCMakeCommand()
+{
+    return _CMAKE_COMMAND;
+}
+
+char const* GitRevision::GetBuildDirectory()
+{
+    return _BUILD_DIRECTORY;
+}
+
 char const* GitRevision::GetSourceDirectory()
 {
     return _SOURCE_DIRECTORY;
@@ -71,13 +81,3 @@ char const* GitRevision::GetProductVersionStr()
 {
     return VER_PRODUCTVERSION_STR;
 }
-
-char const* GitRevision::GetCompilerCFlags()
-{
-    return COMPILER_C_FLAGS;
-}
-
-char const* GitRevision::GetCompilerCXXFlags()
-{
-    return COMPILER_CXX_FLAGS;
-}