auto/otel: Make use of nxt_feature_name

When building with --otel on macOS for example I was seeing compile
failures with the cpu_set_t stuff which should only be used under Linux.

It turned out that despite

  checking for Linux sched_getaffinity() ... not found

we were getting

  #ifndef NXT_HAVE_LINUX_SCHED_GETAFFINITY
  #define NXT_HAVE_LINUX_SCHED_GETAFFINITY  1
  #endif

in build/include/nxt_auto_config.h

It seems this was due to the

    . auto/feature

in auto/otel, this check happens right after the above. Without having

    nxt_feature_name=NXT_HAVE_OTEL

set.

Instead we were adding the define for that manually.

Doing auto/feature without having a nxt_feature_name must have used the
last set one and enabled it.

Set nxt_feature_name and remove the manual editing of nxt_auto_config.h

Fixes: 9d3dcb8 ("otel: add build tooling to include otel code")
Signed-off-by: Andrew Clayton <a.clayton@nginx.com>

Author: ac000

auto/otel

@@ -22,6 +22,7 @@ if [ $NXT_OTEL = YES ]; then
     $echo -n "  - "
 
     nxt_feature="OpenSSL library"
+    nxt_feature_name=NXT_HAVE_OTEL
     nxt_feature_run=yes
     nxt_feature_incs=
     nxt_feature_libs="-lssl -lcrypto"
@@ -42,11 +43,4 @@ if [ $NXT_OTEL = YES ]; then
 
     NXT_OTEL_LIBS="-lssl -lcrypto"
 
-    cat << END >> $NXT_AUTO_CONFIG_H
-
-#ifndef NXT_HAVE_OTEL
-#define NXT_HAVE_OTEL 1
-#endif
-
-END
 fi