libc: newlib revision daf48a0d3 with various space-saving measures:

* --enable-newlib-reent-small
* Compiled with -DHAVE_ABORT -DHAVE_SIGNAL
* Default fd buffer size shrunk to 128 bytes (ref #52)

Full build options:
../configure --with-newlib --enable-multilib --disable-newlib-io-c99-formats --disable-newlib-io-long-long --disable-newlib-io-float --disable-newlib-io-long-double --enable-newlib-supplied-syscalls --enable-target-optspace --program-transform-name="s&^&xtensa-lx106-elf-&" --disable-option-checking --with-target-subdir=xtensa-lx106-elf --target=xtensa-lx106-elf --prefix=/home/gus/dev/esp/rtos/open-rtos/libc/ --enable-newlib-nano-malloc --enable-newlib-nano-formatted-io --enable-newlib-reent-small
CROSS_CFLAGS="-DSIGNAL_PROVIDED -DABORT_PROVIDED" make

libc/xtensa-lx106-elf/include/newlib.h

@@ -31,7 +31,7 @@
 
 /* Optional reentrant struct support.  Used mostly on platforms with
    very restricted storage.  */
-/* #undef _WANT_REENT_SMALL */
+#define _WANT_REENT_SMALL 1
 
 /* Multibyte supported */
 /* #undef _MB_CAPABLE */

libc/xtensa-lx106-elf/include/sys/config.h

@@ -188,6 +188,8 @@
 #ifdef __XTENSA__
 #include <xtensa/config/core-isa.h>
 #define MALLOC_ALIGNMENT ((XCHAL_DATA_WIDTH) < 16 ? 16 : (XCHAL_DATA_WIDTH))
+/* esp8266-specific: shrink the default fd buffer size */
+#define __BUFSIZ__ 128
 #endif
 
 /* This block should be kept in sync with GCC's limits.h.  The point