CMake: don't enable CXX unless building tests/benchmarks

We only need CXX support when building tests/benchmarks.

Fixes:
CMake Error at CMakeLists.txt:6 (PROJECT):
  No CMAKE_CXX_COMPILER could be found.

  Tell CMake where to find the compiler by setting either the environment
  variable "CXX" or the CMake cache entry CMAKE_CXX_COMPILER to the full path
  to the compiler, or to the compiler name if it is in the PATH.

Signed-off-by: James Hilliard <[email protected]>

CMakeLists.txt

@@ -1,14 +1,18 @@
 CMAKE_MINIMUM_REQUIRED(VERSION 3.16 FATAL_ERROR)
 
 # ---[ Project
-PROJECT(FP16 C CXX)
+PROJECT(FP16 C)
 
 # ---[ Options.
 OPTION(FP16_BUILD_TESTS "Build FP16 unit tests" ON)
 OPTION(FP16_BUILD_BENCHMARKS "Build FP16 micro-benchmarks" ON)
 OPTION(FP16_BUILD_COMPARATIVE_BENCHMARKS "Build FP16 micro-benchmarks comparing to alternatives" OFF)
 
 # ---[ CMake options
+IF(FP16_BUILD_TESTS OR FP16_BUILD_BENCHMARKS)
+  ENABLE_LANGUAGE(CXX)
+ENDIF()
+
 IF(FP16_BUILD_TESTS)
   ENABLE_TESTING()
 ENDIF()