set default stack size to 16kb for noMMU

target/arm/uclibc-ng-nommu.config

@@ -78,7 +78,7 @@ UCLIBC_CTOR_DTOR=y
 HAS_NO_THREADS=y
 # UCLIBC_HAS_LINUXTHREADS is not set
 # UCLIBC_HAS_THREADS_NATIVE is not set
-PTHREADS_STACK_DEFAULT_SIZE=2097152
+PTHREADS_STACK_DEFAULT_SIZE=16384
 UCLIBC_HAS_SYSLOG=y
 UCLIBC_HAS_LFS=y
 MALLOC=y