Remove -Werror from Makefile

glibc-2.20 includes some changes to the include/features.h file
introduced by this commit:

  https://sourceware.org/git/?p=glibc.git;a=commit;h=ade40b10ff5fa59a318cf55b9d8414b758e8df78

Those changes make libsvgtiny fail because some warnings are thrown and
the build system is using the -Werror option. We disable this to be able
to build it, or otherwise we will see errors like this one:

GPERF: src/colors.gperf
COMPILE: build-Linux-Linux-release-lib-static/src_colors.c
In file included from
/br/output/host/usr/mipsel-buildroot-linux-gnu/sysroot/usr/include/string.h:25:0,
		 from src/colors.gperf:16:
/br/output/host/usr/mipsel-buildroot-linux-gnu/sysroot/usr/include/features.h:148:3:
error: #warning "_BSD_SOURCE and _SVID_SOURCE are deprecated, use
_DEFAULT_SOURCE" [-Werror=cpp]

and this one:

In file included from src/colors.gperf:18:0:
/home/ldap/vriera/work/mips-buildroots/mips32/output/build/libsvgtiny-12121/src/svgtiny_internal.h:71:0:
error: "strndup" redefined [-Werror]

Signed-off-by: Vicente Olivert Riera <Vincent.Riera@imgtec.com>

diff -rup a/Makefile b/Makefile
--- a/Makefile	2010-01-03 23:37:39.000000000 +0000
+++ b/Makefile	2014-12-11 11:35:37.241903884 +0000
@@ -13,12 +13,6 @@ TESTRUNNER := $(ECHO)
 WARNFLAGS := -Wall -W -Wundef -Wpointer-arith -Wcast-align \
 	-Wwrite-strings -Wstrict-prototypes -Wmissing-prototypes \
 	-Wmissing-declarations -Wnested-externs -pedantic
-# BeOS/Haiku/AmigaOS4 standard library headers create warnings
-ifneq ($(TARGET),beos)
-  ifneq ($(TARGET),AmigaOS)
-    WARNFLAGS := $(WARNFLAGS) -Werror
-  endif
-endif
 CFLAGS := -D_BSD_SOURCE -I$(CURDIR)/include/ \
 	-I$(CURDIR)/src $(WARNFLAGS) $(CFLAGS)
 ifneq ($(GCCVER),2)