Add a clang build target for linux-x86_64

This change documents the world as-is, by turning all warnings on,
and then turning warnings that trigger off again.

Reviewed-by: Andy Polyakov <appro@openssl.org>
Reviewed-by: Richard Levitte <levitte@openssl.org>
diff --git a/Configure b/Configure
index 6246822..8756dcb 100755
--- a/Configure
+++ b/Configure
@@ -107,6 +107,8 @@
 
 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 -DOPENSSL_NO_DEPRECATED";
 
+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";
+
 my $strict_warnings = 0;
 
 my $x86_gcc_des="DES_PTR DES_RISC1 DES_UNROLL";
@@ -398,6 +400,7 @@
 "linux-ia64",	"gcc:-DL_ENDIAN -DTERMIO -O3 -Wall::-D_REENTRANT::-ldl:SIXTY_FOUR_BIT_LONG RC4_CHUNK DES_UNROLL DES_INT:${ia64_asm}:dlfcn:linux-shared:-fPIC::.so.\$(SHLIB_MAJOR).\$(SHLIB_MINOR)",
 "linux-ia64-icc","icc:-DL_ENDIAN -DTERMIO -O2 -Wall::-D_REENTRANT::-ldl -no_cpprt:SIXTY_FOUR_BIT_LONG RC4_CHUNK DES_RISC1 DES_INT:${ia64_asm}:dlfcn:linux-shared:-fPIC::.so.\$(SHLIB_MAJOR).\$(SHLIB_MINOR)",
 "linux-x86_64",	"gcc:-m64 -DL_ENDIAN -DTERMIO -O3 -Wall::-D_REENTRANT::-ldl:SIXTY_FOUR_BIT_LONG RC4_CHUNK DES_INT DES_UNROLL:${x86_64_asm}:elf:dlfcn:linux-shared:-fPIC:-m64:.so.\$(SHLIB_MAJOR).\$(SHLIB_MINOR):::64",
+"linux-x86_64-clang",	"clang: -m64 -DL_ENDIAN -DTERMIO -O3 -Weverything $clang_disabled_warnings -Qunused-arguments::-D_REENTRANT::-ldl:SIXTY_FOUR_BIT_LONG RC4_CHUNK DES_INT DES_UNROLL:${x86_64_asm}:elf:dlfcn:linux-shared:-fPIC:-m64:.so.\$(SHLIB_MAJOR).\$(SHLIB_MINOR):::64",
 "linux-x86_64-icc", "icc:-DL_ENDIAN -DTERMIO -O2::-D_REENTRANT::-ldl -no_cpprt:SIXTY_FOUR_BIT_LONG RC4_CHUNK DES_INT DES_UNROLL:${x86_64_asm}:elf:dlfcn:linux-shared:-fPIC::.so.\$(SHLIB_MAJOR).\$(SHLIB_MINOR):::64",
 "linux-x32",	"gcc:-mx32 -DL_ENDIAN -DTERMIO -O3 -Wall::-D_REENTRANT::-ldl:SIXTY_FOUR_BIT RC4_CHUNK_LL DES_INT DES_UNROLL:${x86_64_asm}:elf:dlfcn:linux-shared:-fPIC:-mx32:.so.\$(SHLIB_MAJOR).\$(SHLIB_MINOR):::x32:",
 "linux64-s390x",	"gcc:-m64 -DB_ENDIAN -DTERMIO -O3 -Wall::-D_REENTRANT::-ldl:SIXTY_FOUR_BIT_LONG RC4_CHAR RC4_CHUNK DES_INT DES_UNROLL:${s390x_asm}:64:dlfcn:linux-shared:-fPIC:-m64:.so.\$(SHLIB_MAJOR).\$(SHLIB_MINOR):::64",
@@ -1649,7 +1652,7 @@
 if ($strict_warnings)
 	{
 	my $wopt;
-	die "ERROR --strict-warnings requires gcc" unless ($cc =~ /gcc$/);
+	die "ERROR --strict-warnings requires gcc or clang" unless ($cc =~ /gcc$/ or $cc =~ /clang$/);
 	foreach $wopt (split /\s+/, $gcc_devteam_warn)
 		{
 		$cflags .= " $wopt" unless ($cflags =~ /$wopt/)