Fix duplicated stc=gnu99/c17 in build

Author: earlephilhower

cores/esp8266/core_esp8266_postmortem.cpp

@@ -149,7 +149,7 @@ void __wrap_system_restart_local() {
         ets_printf_P(PSTR("\nSoft WDT reset\n"));
     }
     else if (rst_info.reason == REASON_USER_STACK_SMASH) {
-        ets_printf_P(PSTR("\nStack corrupted, stack smash detected.\n"));
+        ets_printf_P(PSTR("\nStack overflow detected.\n"));
    }
     else {
         ets_printf_P(PSTR("\nGeneric Reset\n"));
@@ -297,7 +297,7 @@ void __panic_func(const char* file, int line, const char* func) {
 uintptr_t __stack_chk_guard = 0x08675309 ^ RANDOM_REG32;
 void __stack_chk_fail(void) {
     s_user_reset_reason = REASON_USER_STACK_SMASH;
-    ets_printf_P(PSTR("\nGCC detected stack overrun"));
+    ets_printf_P(PSTR("\nPANIC: Stack overrun"));
 
     if (gdb_present())
         __asm__ __volatile__ ("syscall"); // triggers GDB when enabled

platform.txt

@@ -55,7 +55,7 @@ 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}/{build.lwip_include}" "-I{compiler.libc.path}/include" "-I{build.path}/core"
 
 compiler.c.cmd=xtensa-lx106-elf-gcc
-compiler.c.flags=-c {compiler.warning_flags} -std=c17 {build.stacksmash_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 {build.exception_flags} {build.sslflags}
+compiler.c.flags=-c {compiler.warning_flags} -std=c17 {build.stacksmash_flags} -Os -g -Wpointer-arith -Wno-implicit-function-declaration -Wl,-EL -fno-inline-functions -nostdlib -mlongcalls -mtext-section-literals -falign-functions=4 -MMD -ffunction-sections -fdata-sections {build.exception_flags} {build.sslflags}
 
 compiler.S.cmd=xtensa-lx106-elf-gcc
 compiler.S.flags=-c -g -x assembler-with-cpp -MMD -mlongcalls