BaseTools: Remove -Wno-unneeded-internal-declaration from CLANGDWARF

Subsequent to updating the 'null' DEBUG macro to explicitly
discard its expression, it is possible to remove this warning
suppression from CLANGDWARF and still successfully compile
its RELEASE build.

Note that CLANGPDB did and does not have this warning suppressed,
and so before updating the 'null' DEBUG macro, CLANGPDB RELEASE
was not building successfully in recent versions of clang,
but was stopping with the error:

.../edk2/OvmfPkg/VirtioSerialDxe/VirtioSerial.c:28:22: error:
variable 'EventNames' is not needed and will not be
emitted [-Werror,-Wunneeded-internal-declaration]
STATIC CONST CHAR8  *EventNames[] = {
                     ^

This change makes the two CLANG variants match with respect
to this warning, and leaves the warning enabled which is
considered a benefit as it has the potential to catch real
coding errors

Signed-off-by: Mike Beaton <[email protected]>

BaseTools/Conf/tools_def.template

@@ -2017,7 +2017,7 @@ DEFINE CLANGDWARF_X64_DLINK2_FLAGS        = -Wl,--defsym=PECOFF_HEADER_SIZE=0x22
 DEFINE CLANGDWARF_IA32_TARGET             = -target i686-pc-linux-gnu
 DEFINE CLANGDWARF_X64_TARGET              = -target x86_64-pc-linux-gnu
 
-DEFINE CLANGDWARF_WARNING_OVERRIDES    = -Wno-parentheses-equality -Wno-empty-body -Wno-unused-const-variable -Wno-varargs -Wno-unknown-warning-option -Wno-unused-but-set-variable -Wno-unused-const-variable -Wno-unaligned-access -Wno-unneeded-internal-declaration
+DEFINE CLANGDWARF_WARNING_OVERRIDES    = -Wno-parentheses-equality -Wno-empty-body -Wno-unused-const-variable -Wno-varargs -Wno-unknown-warning-option -Wno-unused-but-set-variable -Wno-unused-const-variable -Wno-unaligned-access
 DEFINE CLANGDWARF_ALL_CC_FLAGS         = DEF(GCC48_ALL_CC_FLAGS) DEF(CLANGDWARF_WARNING_OVERRIDES) -fno-stack-protector -mms-bitfields -Wno-address -Wno-shift-negative-value -Wno-unknown-pragmas -Wno-incompatible-library-redeclaration -fno-asynchronous-unwind-tables -mno-sse -mno-mmx -msoft-float -mno-implicit-float  -ftrap-function=undefined_behavior_has_been_optimized_away_by_clang -funsigned-char -fno-ms-extensions -Wno-null-dereference
 
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