package/glibc: can't be built without optimization

Fix the following build failure:

In file included from <command-line>:
./../include/libc-symbols.h:75:3: error: #error "glibc cannot be compiled without optimization"
   75 | # error "glibc cannot be compiled without optimization"
      |   ^~~~~

Fixes:
 - http://autobuild.buildroot.org/results/1ba20982d5ec0edc751a11a2d5639f5f6477b9bc

Signed-off-by: Fabrice Fontaine <fontaine.fabrice@gmail.com>
Signed-off-by: Yann E. MORIN <yann.morin.1998@free.fr>

package/glibc/glibc.mk

@@ -118,6 +118,11 @@ ifeq ($(BR2_nios2),y)
 GLIBC_CFLAGS += -O2
 endif
 
+# glibc can't be built without optimization
+ifeq ($(BR2_OPTIMIZE_0),y)
+GLIBC_CFLAGS += -O1
+endif
+
 # glibc can't be built with Optimize for fast
 ifeq ($(BR2_OPTIMIZE_FAST),y)
 GLIBC_CFLAGS += -O2