libubacktrace: fix build due to some typos

Commit 71c10c484e7dc113396cccb7e503befb759c6346 broke libubactrace build
due to some typos, so that backtrace.o[sS] were not built.
This definetively fixes this problem.

Signed-off-by: Filippo Arcidiacono <filippo.arcidiacono@st.com>
Signed-off-by: Carmelo Amoroso <carmelo.amoroso@st.com>
libc: elf: explicitly include uClibc_page.h to make PAGE_SIZE visible

Signed-off-by: Filippo Arcidiacono <filippo.arcidiacono@st.com>
Signed-off-by: Carmelo Amoroso <carmelo.amoroso@st.com>