[llvm-config] Remove --src-root option

Remove the `--src-root` option from the deprecated llvm-config tool.
None of the llvm-project projects use this option anymore. The value
was only meaningful for in-tree use and usually became no longer correct
once LLVM was installed -- either because it was built in a temporary
directory, or installed from a binary package and built on a different
system entirely.  Therefore, third-party tools could not have been
relying on it anyway.

The LLVM_SRC_ROOT #define is left intact, as it is used to compute
includedir when llvm-config is used in-source.

Differential Revision: https://reviews.llvm.org/D137144

llvm/docs/CommandGuide/llvm-config.rst

@@ -130,10 +130,6 @@ OPTIONS
 
  Print how the provided components can be collectively linked (`shared` or `static`).
 
-**--src-root**
-
- Print the source root from which LLVM was built.
-
 **--system-libs**
 
  Print all the system libraries needed to link against the specified LLVM

llvm/tools/llvm-config/llvm-config.cpp

@@ -234,7 +234,6 @@ Options:\n\
   --obj-root        Print the object root used to build LLVM.\n\
   --prefix          Print the installation prefix.\n\
   --shared-mode     Print how the provided components can be collectively linked (`shared` or `static`).\n\
-  --src-root        Print the source root LLVM was built from.\n\
   --system-libs     System Libraries needed to link against LLVM components.\n\
   --targets-built   List of all targets currently built.\n\
   --version         Print LLVM version.\n\
@@ -592,8 +591,6 @@ int main(int argc, char **argv) {
         PrintSharedMode = true;
       } else if (Arg == "--obj-root") {
         OS << ActivePrefix << '\n';
-      } else if (Arg == "--src-root") {
-        OS << LLVM_SRC_ROOT << '\n';
       } else if (Arg == "--ignore-libllvm") {
         LinkDyLib = false;
         LinkMode = BuiltSharedLibs ? LinkModeShared : LinkModeAuto;