tools: Stop re-defining -std= when building tools

While we intentionally set -std=gnu11 for building host tools, and have
for quite some time, we never dropped -std=gnu99 from tools/Makefile.
This resulted in passing -std=gnu11 ... -std=gnu99 when building, and
gnu99 would win.  This in turn would result now in warnings such as:
tools/mkeficapsule.c:25:15: warning: redefinition of typedef 'u32' is a C11 feature [-Wtypedef-redefinition]
typedef __u32 u32;
              ^

Signed-off-by: Tom Rini <trini@konsulko.com>

Makefile

@@ -299,9 +299,7 @@ KBUILD_HOSTLDLIBS   := $(HOST_LFS_LIBS) $(HOSTLDLIBS)
 # have older compilers as their default, so we make it explicit for
 # these that our host tools are GNU11 (i.e. C11 w/ GNU extensions).
 CSTD_FLAG := -std=gnu11
-ifeq ($(HOSTOS),linux)
 KBUILD_HOSTCFLAGS += $(CSTD_FLAG)
-endif
 
 ifeq ($(HOSTOS),cygwin)
 KBUILD_HOSTCFLAGS	+= -ansi

tools/Makefile

@@ -295,8 +295,7 @@ HOST_EXTRACFLAGS += -include $(srctree)/include/compiler.h \
 		-I$(srctree)/tools \
 		-DUSE_HOSTCC \
 		-D__KERNEL_STRICT_NAMES \
-		-D_GNU_SOURCE \
-		-std=gnu99
+		-D_GNU_SOURCE
 
 __build:	$(LOGO-y)