add argument check in setenv()
add argument check in setenv()

setenv() in glibc/eglibc will check the argument, like this,
  ...
  if (name == NULL || *name == '\0' || strchr (name, '=') != NULL)
    {
      __set_errno (EINVAL);
      return -1;
    }
  ...
So add argument check in uclibc's setenv() too.

Signed-off-by: Xishi Qiu <dd58e6c73de42ea3812c4e45cc983f071455d7f2@huawei.com>
Signed-off-by: Bernhard Reutner-Fischer <ce1ac9e9ad16abccd7821f371ad381197b4768ac@gmail.com>

kraj/uClibc,kraj/uClibc,wbx-github/uclibc-ng,majek/uclibc-vx32,kraj/uclibc-ng,majek/uclibc-vx32,kraj/uclibc-ng,wbx-github/uclibc-ng,foss-for-synopsys-dwc-arc-processors/uClibc,foss-for-synopsys-dwc-arc-processors/uClibc,majek/uclibc-vx32,majek/uclibc-vx32,kraj/uclibc-ng,brgl/uclibc-ng,kraj/uClibc,brgl/uclibc-ng,foss-for-synopsys-dwc-arc-processors/uClibc,wbx-github/uclibc-ng,kraj/uClibc,foss-for-synopsys-dwc-arc-processors/uClibc,brgl/uclibc-ng,kraj/uclibc-ng,wbx-github/uclibc-ng,brgl/uclibc-ng