[Build] Remove Differentiation without tgmath (#34409)

Reverts #34116 -- this is no longer needed.

This reverts commit b972bef.

Author: edymtt

stdlib/CMakeLists.txt

@@ -69,10 +69,6 @@ option(SWIFT_STDLIB_OS_VERSIONING
     "Build stdlib with availability based on OS versions (Darwin only)."
     TRUE)
 
-option(SWIFT_COMPILE_DIFFERENTIATION_WITHOUT_TGMATH
-       "Build Differentation without tgmath (and dependency on platform runtime libraries)"
-       FALSE)
-
 #
 # End of user-configurable options.
 #

stdlib/public/CMakeLists.txt

@@ -91,15 +91,7 @@ if(SWIFT_BUILD_STDLIB)
   add_subdirectory(SwiftOnoneSupport)
 
   if(SWIFT_ENABLE_EXPERIMENTAL_DIFFERENTIABLE_PROGRAMMING)
-    if(SWIFT_COMPILE_DIFFERENTIATION_WITHOUT_TGMATH)
-      # Use a different CMakeLists.txt for this configuration
-      # while sharing the bulk of the code
-      # This way we will reduce any side effect on the main configuration
-      # and increase the readability of the CMake code
-      add_subdirectory(Differentiation_NoTgMath)
-    else()
-      add_subdirectory(Differentiation)
-    endif()
+    add_subdirectory(Differentiation)
   endif()
 
   if(SWIFT_ENABLE_EXPERIMENTAL_CONCURRENCY)