Switch to custom newlib build

Built from https://github.com/igrr/newlib-xtensa using:
./configure --with-newlib --enable-multilib --disable-newlib-io-c99-formats --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 --enable-newlib-nano-formatted-io --enable-newlib-reent-small  --prefix=path-to-arduino-core/tools/sdk/libc
CROSS_CFLAGS="-DMALLOC_PROVIDED -DSIGNAL_PROVIDED -DABORT_PROVIDED" make
make install

Author: igrr

platform.txt

@@ -19,18 +19,19 @@ compiler.warning_flags.all=-Wall -Wextra
 
 compiler.path={runtime.tools.xtensa-lx106-elf-gcc.path}/bin/
 compiler.sdk.path={runtime.platform.path}/tools/sdk
-compiler.cpreprocessor.flags=-D__ets__ -DICACHE_FLASH -U__STRICT_ANSI__ "-I{compiler.sdk.path}/include" "-I{compiler.sdk.path}/lwip/include"
+compiler.libc.path={runtime.platform.path}/tools/sdk/libc/xtensa-lx106-elf
+compiler.cpreprocessor.flags=-D__ets__ -DICACHE_FLASH -U__STRICT_ANSI__ "-I{compiler.sdk.path}/include" "-I{compiler.sdk.path}/lwip/include" "-I{compiler.libc.path}/include"
 
 compiler.c.cmd=xtensa-lx106-elf-gcc
 compiler.c.flags=-c {compiler.warning_flags} -Os -g -Wpointer-arith -Wno-implicit-function-declaration -Wl,-EL -fno-inline-functions -nostdlib -mlongcalls -mtext-section-literals -falign-functions=4 -MMD -std=gnu99 -ffunction-sections -fdata-sections
 
 compiler.S.cmd=xtensa-lx106-elf-gcc
 compiler.S.flags=-c -g -x assembler-with-cpp -MMD -mlongcalls
 
-compiler.c.elf.flags=-g {compiler.warning_flags} -Os -nostdlib -Wl,--no-check-sections -u call_user_start -Wl,-static "-L{compiler.sdk.path}/lib" "-L{compiler.sdk.path}/ld" "-T{build.flash_ld}" -Wl,--gc-sections -Wl,-wrap,system_restart_local -Wl,-wrap,register_chipv6_phy
+compiler.c.elf.flags=-g {compiler.warning_flags} -Os -nostdlib -Wl,--no-check-sections -u call_user_start -Wl,-static "-L{compiler.sdk.path}/lib" "-L{compiler.sdk.path}/ld" "-L{compiler.libc.path}/lib" "-T{build.flash_ld}" -Wl,--gc-sections -Wl,-wrap,system_restart_local -Wl,-wrap,register_chipv6_phy
 
 compiler.c.elf.cmd=xtensa-lx106-elf-gcc
-compiler.c.elf.libs=-lhal -lphy -lpp -lnet80211 {build.lwip_lib} -lwpa -lcrypto -lmain -lwps -laxtls -lsmartconfig -lmesh -lwpa2 -lm -lcmin -lgcc 
+compiler.c.elf.libs=-lhal -lphy -lpp -lnet80211 {build.lwip_lib} -lwpa -lcrypto -lmain -lwps -laxtls -lsmartconfig -lmesh -lwpa2 -lm -lc -lgcc
 
 compiler.cpp.cmd=xtensa-lx106-elf-g++
 compiler.cpp.flags=-c {compiler.warning_flags} -Os -g -mlongcalls -mtext-section-literals -fno-exceptions -fno-rtti -falign-functions=4 -std=c++11 -MMD -ffunction-sections -fdata-sections

tools/sdk/ld/eagle.app.v6.common.ld

@@ -153,7 +153,7 @@ SECTIONS
     *.c.o( EXCLUDE_FILE (umm_malloc.c.o) .literal*, \
            EXCLUDE_FILE (umm_malloc.c.o) .text*)
     *.cpp.o(.literal*, .text*)
-    *libcmin.a:(.literal .text .literal.* .text.*)
+    *libc.a:(.literal .text .literal.* .text.*)
     *libm.a:(.literal .text .literal.* .text.*)
     *libgcc.a:_umoddi3.o(.literal .text)
     *libgcc.a:_udivdi3.o(.literal .text)