CMake: quiet build warnings from fmtlib

Reference fmtlib as a system include to suppress noisy messages.

extern/fmtlib/CMakeLists.txt

@@ -3,10 +3,10 @@
 # SPDX-License-Identifier: GPL-2.0-or-later
 
 set(INC
-  PUBLIC include
 )
 
 set(INC_SYS
+  PUBLIC include
 )
 
 set(SRC

source/blender/animrig/CMakeLists.txt

@@ -8,12 +8,12 @@ set(INC
 
   ../editors/include
   ../makesrna
-  ../../../extern/fmtlib/include
   # RNA_prototypes.hh
   ${CMAKE_BINARY_DIR}/source/blender/makesrna
 )
 
 set(INC_SYS
+  ../../../extern/fmtlib/include
 )
 
 set(SRC

source/blender/editors/animation/CMakeLists.txt

@@ -8,12 +8,12 @@ set(INC
   ../space_graph
   ../../asset_system
   ../../makesrna
-  ../../../../extern/fmtlib/include
   # RNA_prototypes.hh
   ${CMAKE_BINARY_DIR}/source/blender/makesrna
 )
 
 set(INC_SYS
+  ../../../../extern/fmtlib/include
 )
 
 set(SRC

source/blender/editors/screen/CMakeLists.txt

@@ -8,12 +8,12 @@ set(INC
   ../space_graph
   ../../makesrna
   ../../nodes
-  ../../../../extern/fmtlib/include
   # RNA_prototypes.hh
   ${CMAKE_BINARY_DIR}/source/blender/makesrna
 )
 
 set(INC_SYS
+  ../../../../extern/fmtlib/include
 )
 
 set(SRC

source/blender/editors/space_outliner/CMakeLists.txt

@@ -6,14 +6,12 @@ set(INC
   ../include
   ../../blenfont
   ../../makesrna
-
-  ../../../../extern/fmtlib/include
-
   # RNA_prototypes.hh
   ${CMAKE_BINARY_DIR}/source/blender/makesrna
 )
 
 set(INC_SYS
+  ../../../../extern/fmtlib/include
 )
 
 set(SRC

source/blender/io/grease_pencil/CMakeLists.txt

@@ -10,10 +10,10 @@ set(INC
   ../../makesrna
   ../../../../intern/guardedalloc
   ../../../../intern/utfconv
-  ../../../../extern/fmtlib/include
 )
 
 set(INC_SYS
+  ../../../../extern/fmtlib/include
 )
 
 set(SRC

source/blender/makesrna/intern/CMakeLists.txt

@@ -263,7 +263,6 @@ set(INC
   ../../render
   ../../../../intern/clog
   ../../../../intern/cycles/blender
-  ../../../../extern/fmtlib/include
   ../../../../intern/memutil
   ../../../../intern/mantaflow/extern
 
@@ -273,7 +272,7 @@ set(INC
 )
 
 set(INC_SYS
-
+  ../../../../extern/fmtlib/include
 )
 
 if(WITH_CYCLES)