GMP/macOS: silence "PIE disabled" linker warning.

The change builds GMP with `--with-pic` flag on non-arm architecture.

The warning:
ld: warning: PIE disabled. Absolute addressing
(perhaps -mdynamic-no-pic) not allowed in code signed PIE, but used in
___gmpn_divexact_1 from lib/darwin/gmp/lib/libgmp.a(dive_1.o). To fix
this warning, don't compile with -mdynamic-no-pic or link with
-Wl,-no_pie

Reviewed By: sebbas

Differential Revision: https://developer.blender.org/D8823

build_files/build_environment/cmake/gmp.cmake

@@ -25,11 +25,18 @@ else()
   set(GMP_OPTIONS --enable-static --disable-shared )
 endif()
 
-if(APPLE AND ("${CMAKE_OSX_ARCHITECTURES}" STREQUAL "arm64"))
-  set(GMP_OPTIONS
-     ${GMP_OPTIONS}
-     --disable-assembly
-  )
+if(APPLE)
+  if("${CMAKE_OSX_ARCHITECTURES}" STREQUAL "arm64")
+    set(GMP_OPTIONS
+      ${GMP_OPTIONS}
+      --disable-assembly
+    )
+  else()
+    set(GMP_OPTIONS
+      ${GMP_OPTIONS}
+      --with-pic
+    )
+  endif()
 endif()
 
 ExternalProject_Add(external_gmp