Changes

contrib/jenkins: fix running "make distcheck"

Fix for the following, seen with debian 13 and CFLAGS=-g:

  /usr/bin/ld: rtl_test.o: undefined reference to symbol 'round@@GLIBC_2.2.5'
  /usr/bin/ld: /lib/x86_64-linux-gnu/libm.so.6: error adding symbols: DSO missing from command line

This happens, because "make distcheck" runs ./configure with -Werror and
then gets an incorrect result at "checking for sqrt in -lm". Afterwards
it tries to link rtl_test without -lm.

Correct:

  configure:14090: checking for sqrt in -lm
  configure:14119: gcc -o conftest -g -I/usr/include/libusb-1.0    conftest.c -lm   -lusb-1.0  -lpthread -lm >&5
  conftest.c:35:6: warning: conflicting types for built-in function 'sqrt'; expected 'double(double)' [-Wbuiltin-declaration-mismatch]
     35 | char sqrt (void);
        |      ^~~~
  conftest.c:1:1: note: 'sqrt' is declared in header '<math.h>'
      1 | /* confdefs.h */
  configure:14119: $? = 0
  configure:14131: result: yes

Failing in "make distcheck" due to -Werror:

  configure:14041: checking for atan2 in -lm
  configure:14070: gcc -o conftest -g -I/usr/include/libusb-1.0  -fsanitize=address -fsanitize=undefined -Werror -Wno-error=deprecated -Wno-error=deprecated-declarations -Wno-error=cpp -Wall -Wextra -Wno-unused-parameter -Wno-unused -Wsign-compare -Wdeclaration-after-statement -I/usr/include/libusb-1.0    conftest.c -lm   -lusb-1.0  -lpthread >&5
  conftest.c:35:6: error: conflicting types for built-in function 'atan2'; expected 'double(double,  double)' [-Werror=builtin-declaration-mismatch]
     35 | char atan2 (void);
        |      ^~~~~
  conftest.c:1:1: note: 'atan2' is declared in header '<math.h>'
      1 | /* confdefs.h */
  cc1: all warnings being treated as errors
  configure:14070: $? = 1
  configure: failed program was:
  …
  configure:14082: result: no

Fix this by running ./configure without --enable-werror before running
"make distcheck".

Related: https://bug-libtool.gnu.narkive.com/YrSM40bs/lt-lib-m-and-gcc
Change-Id: I3aaf21f9fb9ee20409968c7a9160a252d65c8d57