[libc][NFC] Clean up test/src/math/differential_testing folder, renaming it to performance_testing. (#84646)

Removing all the diff tests.

Author: lntue

libc/docs/math/index.rst

@@ -567,13 +567,13 @@ Legends:
 Performance
 ===========
 
-* Simple performance testings are located at: `libc/test/src/math/differential_testing <https://github.com/llvm/llvm-project/tree/main/libc/test/src/math/differential_testing>`_.
+* Simple performance testings are located at: `libc/test/src/math/performance_testing <https://github.com/llvm/llvm-project/tree/main/libc/test/src/math/performance_testing>`_.
 
 * We also use the *perf* tool from the `CORE-MATH <https://core-math.gitlabpages.inria.fr/>`_
   project: `link <https://gitlab.inria.fr/core-math/core-math/-/tree/master>`_.
   The performance results from the CORE-MATH's perf tool are reported in the
   table below, using the system library as reference (such as the `GNU C library <https://www.gnu.org/software/libc/>`_
-  on Linux). Fmod performance results obtained with "differential_testing".
+  on Linux). Fmod performance results obtained with "performance_testing".
 
 +--------------+-------------------------------+-------------------------------+-------------------------------------+----------------------------------------------------------------------+
 | <Func>       | Reciprocal throughput (clk)   | Latency (clk)                 | Testing ranges                      | Testing configuration                                                |

libc/src/math/docs/add_math_function.md

@@ -129,11 +129,11 @@ implementation (which is very often glibc).
 
 - Add a performance test to:
 ```
-  libc/test/src/math/differential_testing/<func>_perf.cpp
+  libc/test/src/math/performance_testing/<func>_perf.cpp
 ```
 - Add the corresponding entry point to:
 ```
-  libc/test/src/math/differential_testing/CMakeLists.txt
+  libc/test/src/math/performance_testing/CMakeLists.txt
 ```
 
 ## Build and Run
@@ -189,8 +189,8 @@ implementation (which is very often glibc).
 
 - Build and Run performance test:
 ```
-  $ ninja libc.test.src.math.differential_testing.<func>_perf
-  $ projects/libc/test/src/math/differential_testing/libc.test.src.math.differential_testing.<func>_perf
+  $ ninja libc.test.src.math.performance_testing.<func>_perf
+  $ projects/libc/test/src/math/performance_testing/libc.test.src.math.performance_testing.<func>_perf
   $ cat <func>_perf.log
 ```
 

libc/test/src/math/CMakeLists.txt

@@ -1721,5 +1721,5 @@ add_subdirectory(smoke)
 
 if(NOT LLVM_LIBC_FULL_BUILD)
   add_subdirectory(exhaustive)
-  add_subdirectory(differential_testing)
+  add_subdirectory(performance_testing)
 endif()