Add -DDEBUG_UNUSED to --strict-warnings

In order to receive warnings on unused function return values the flag
-DDEBUG_UNUSED must be passed to the compiler. This change adds that for the
--strict-warnings Configure option.
Reviewed-by: NRichard Levitte <levitte@openssl.org>

Configure

@@ -110,7 +110,7 @@ my $usage="Usage: Configure [no-<cipher> ...] [enable-<cipher> ...] [experimenta
 # Minimum warning options... any contributions to OpenSSL should at least get
 # past these.
 
-my $gcc_devteam_warn = "-Wall -pedantic -DPEDANTIC -Wno-long-long -Wsign-compare -Wmissing-prototypes -Wshadow -Wformat -Werror -DCRYPTO_MDEBUG_ALL -DCRYPTO_MDEBUG_ABORT -DREF_CHECK";
+my $gcc_devteam_warn = "-Wall -pedantic -DPEDANTIC -Wno-long-long -Wsign-compare -Wmissing-prototypes -Wshadow -Wformat -Werror -DCRYPTO_MDEBUG_ALL -DCRYPTO_MDEBUG_ABORT -DREF_CHECK -DDEBUG_UNUSED";
 
 my $clang_disabled_warnings = "-Wno-language-extension-token -Wno-extended-offsetof -Wno-padded -Wno-shorten-64-to-32 -Wno-format-nonliteral -Wno-missing-noreturn -Wno-unused-parameter -Wno-sign-conversion -Wno-unreachable-code -Wno-conversion -Wno-documentation -Wno-missing-variable-declarations -Wno-cast-align -Wno-incompatible-pointer-types-discards-qualifiers -Wno-missing-variable-declarations -Wno-missing-field-initializers -Wno-unused-macros -Wno-disabled-macro-expansion -Wno-conditional-uninitialized -Wno-switch-enum";