ARMC6: disable "reserved user-defined literal" warning

Clang warns about reserved user-defined literals by default. This
warning is not terribly helpful; compilers aren't normally in the
habit of warning about use of reserved identifiers. It can interfere
with, for example, deliberate emulation of a future standard
language feature.

The warning was promoted to an error in an mbed client build, due to a
non-C++11 "%s"name occurring in a macro. But the macro itself was never
invoked, so the misinterpretation as C++11 caused no problems other than
this warning. Killing the warning will let that code build on ARMC6.
The code already built on GCC and IAR.

If that macro ever was used, then a separate error about operator ""
name not being defined would be generated, on all 3 toolchains.

tools/profiles/debug.json

@@ -18,6 +18,7 @@
     "ARMC6": {
         "common": ["-c", "--target=arm-arm-none-eabi", "-mthumb", "-g", "-O1",
                    "-Wno-armcc-pragma-push-pop", "-Wno-armcc-pragma-anon-unions",
+                   "-Wno-reserved-user-defined-literal",
                    "-DMULADDC_CANNOT_USE_R7", "-fdata-sections",
                    "-fno-exceptions", "-MMD", "-D_LIBCPP_EXTERN_TEMPLATE(...)=",
                    "-fshort-enums", "-fshort-wchar", "-DMBED_DEBUG",

tools/profiles/develop.json

@@ -17,6 +17,7 @@
     "ARMC6": {
         "common": ["-c", "--target=arm-arm-none-eabi", "-mthumb", "-Os",
                    "-Wno-armcc-pragma-push-pop", "-Wno-armcc-pragma-anon-unions",
+                   "-Wno-reserved-user-defined-literal",
                    "-DMULADDC_CANNOT_USE_R7", "-fdata-sections",
                    "-fno-exceptions", "-MMD", "-D_LIBCPP_EXTERN_TEMPLATE(...)=",
                    "-fshort-enums", "-fshort-wchar", "-DMBED_TRAP_ERRORS_ENABLED=1"],

tools/profiles/release.json

@@ -17,6 +17,7 @@
     "ARMC6": {
         "common": ["-c", "--target=arm-arm-none-eabi", "-mthumb", "-Oz",
                    "-Wno-armcc-pragma-push-pop", "-Wno-armcc-pragma-anon-unions",
+                   "-Wno-reserved-user-defined-literal",
                    "-DMULADDC_CANNOT_USE_R7", "-fdata-sections",
                    "-fno-exceptions", "-MMD", "-D_LIBCPP_EXTERN_TEMPLATE(...)=",
                    "-fshort-enums", "-fshort-wchar", "-DNDEBUG"],