Double slashes (`//`) appear in installed include paths during CMake install

[BwL1289]

When installing the OpenTelemetry C++ SDK, the generated install paths include redundant double slashes (//) in several include directory entries.

This behavior occurs during the cmake install step and affects the following paths:

-- Up-to-date: /usr/local/include/opentelemetry/exporters//prometheus
-- Up-to-date: /usr/local/include/opentelemetry/exporters//prometheus/exporter_utils.h
-- Up-to-date: /usr/local/include/opentelemetry/exporters//prometheus/exporter_factory.h
-- Up-to-date: /usr/local/include/opentelemetry/exporters//prometheus/exporter.h
-- Up-to-date: /usr/local/include/opentelemetry/exporters//prometheus/collector.h
-- Up-to-date: /usr/local/include/opentelemetry/exporters//prometheus/exporter_options.h

-- Up-to-date: /usr/local/include/opentelemetry//ext
-- Up-to-date: /usr/local/include/opentelemetry//ext/http
-- Up-to-date: /usr/local/include/opentelemetry//ext/http/server
-- Up-to-date: /usr/local/include/opentelemetry//ext/http/server/socket_tools.h
-- Up-to-date: /usr/local/include/opentelemetry//ext/http/server/file_http_server.h
-- Up-to-date: /usr/local/include/opentelemetry//ext/http/server/http_server.h
-- Up-to-date: /usr/local/include/opentelemetry//ext/http/common
-- Up-to-date: /usr/local/include/opentelemetry//ext/http/common/url_parser.h
-- Up-to-date: /usr/local/include/opentelemetry//ext/http/client
-- Up-to-date: /usr/local/include/opentelemetry//ext/http/client/http_client_factory.h
-- Up-to-date: /usr/local/include/opentelemetry//ext/http/client/http_client.h
-- Up-to-date: /usr/local/include/opentelemetry//ext/http/client/curl
-- Up-to-date: /usr/local/include/opentelemetry//ext/http/client/curl/http_client_curl.h
-- Up-to-date: /usr/local/include/opentelemetry//ext/http/client/curl/http_operation_curl.h

Expected Behavior

Install paths should contain a single slash between directory components. For example:

/usr/local/include/opentelemetry/exporters/prometheus
/usr/local/include/opentelemetry/ext/http/client

Actual Behavior

Two consecutive slashes appear in the generated paths (//), suggesting that directory path concatenation may not be sanitized properly during install path generation.

[marcalff]

This is purely cosmetic in the install output. a/b and a//b are equivalent.

[malff@malff-desktop ~]$ cd /usr/local/include
[malff@malff-desktop include]$ pwd
/usr/local/include
[malff@malff-desktop include]$ cd
[malff@malff-desktop ~]$ cd /usr//local///include
[malff@malff-desktop include]$ pwd
/usr/local/include
[malff@malff-desktop include]$