framework: resolve compiler warnings

[dbarry9]

Pull Request Description

When a build is configured with --enable-warnings, there are unused-variable and sign-compare warnings:

papi.c: In function 'PAPI_set_multiplex':
papi.c:4065:13: warning: unused variable 'ret' [-Wunused-variable]
 4065 |         int ret;
           |              ^~~
papi_preset.c: In function 'papi_load_derived_events_component':
papi_preset.c:1648:57: warning: comparison of integer expressions of different signedness: 'int' and 'size_t' {aka 'long unsigned int'} [-Wsign-compare]
 1648 |                 for (pos = component_prefix_offset; pos < strlen(basename); pos++) {
           |                                                                                      ^

This PR resolves these warnings.

These changes have been tested on a system containing the ARM Neoverse-V2 CPU and the NVIDIA GH200 480GB GPU (Grace-Hopper architecture).

Author Checklist

• Description
  Why this PR exists. Reference all relevant information, including background, issues, test failures, etc
• Commits
  Commits are self contained and only do one thing
  Commits have a header of the form: module: short description
  Commits have a body (whenever relevant) containing a detailed description of the addressed problem and its solution
• Tests
  The PR needs to pass all the tests

[dbarry9]

@Treece-Burgess There are also some compiler warnings in the cuda component when --enable-warnings is used, but I wanted to keep the resolution of framework-related compiler warnings to its own PR.

[Treece-Burgess]

When a build is configured with --enable-warnings, there are unused-variable and sign-compare warnings:

I can take care of the cuda component compilation warnings.

[Treece-Burgess]

I have been able to recreate the compilation warnings on Hopper1 at Oregon (CPU: ARM Neoverse V2, GPU: 1 * NVIDIA GH200) with the configure ./configure --prefix=$PWD/test-install --enable-warnings --with-debug=yes:

papi.c:4065:13: warning: unused variable ‘ret’ [-Wunused-variable]
 4065 |         int ret;
papi_preset.c:1648:57: warning: comparison of integer expressions of different signedness: ‘int’ and ‘size_t’ {aka ‘long unsigned int’} [-Wsign-compare]
 1648 |                 for (pos = component_prefix_offset; pos < strlen(basename); pos++) {

This PR resolves the compilation warnings. As a sanity check I ran ./papi_avail and ./papi_command_line PAPI_FP_OPS as this change is made in papi_preset.c. Both functioned as expected.