CMakeLists: Fix building of llvm-with-cov

`target_compile_options` should have been `target_compile_definitions`

Also remove the global `set_cpp_flag` for these defines which are now unnecessary.

Bug: b/145758253
Change-Id: Ie03b0ad196bd1ee155e3f4953d920d6b502db51c
Reviewed-on: https://swiftshader-review.googlesource.com/c/SwiftShader/+/44848
Reviewed-by: Nicolas Capens <nicolascapens@google.com>
Reviewed-by: Antonio Maiorano <amaiorano@google.com>
Kokoro-Result: kokoro <noreply+kokoro@google.com>
Tested-by: Ben Clayton <bclayton@google.com>
diff --git a/CMakeLists.txt b/CMakeLists.txt
index 954b051..7a2d5a6 100644
--- a/CMakeLists.txt
+++ b/CMakeLists.txt
@@ -429,9 +429,6 @@
         "-fno-operator-names"
     )
 
-    # LLVM headers requires these flags to be set
-    set_cpp_flag("-D__STDC_CONSTANT_MACROS -D__STDC_LIMIT_MACROS")
-
     if(ARCH STREQUAL "x86")
         set_cpp_flag("-m32")
         set_cpp_flag("-msse2")
diff --git a/third_party/llvm-10.0/CMakeLists.txt b/third_party/llvm-10.0/CMakeLists.txt
index 3d4d6e5..c201a1f 100644
--- a/third_party/llvm-10.0/CMakeLists.txt
+++ b/third_party/llvm-10.0/CMakeLists.txt
@@ -1250,7 +1250,7 @@
             ${LLVM_INCLUDE_DIR}
     )
 
-    target_compile_options(llvm-with-cov
+    target_compile_definitions(llvm-with-cov
         PUBLIC
             "__STDC_CONSTANT_MACROS"
             "__STDC_LIMIT_MACROS"