fix: ensure installed binaries have executable permissions

[ANAS727189]

Fixes #314

This PR fixes an issue where binaries installed via fpm install (or ./install.sh) did not have the executable bit set (resulting in rw-r--r--), requiring users to manually run chmod +x.

Changes Implemented

• src/fpm_filesystem.F90: Added a set_executable subroutine.
• It uses c_chmod (via iso_c_binding) for standard builds (efficient and standard).
• Includes a fallback to shell chmod +x for the bootstrap phase (#ifdef FPM_BOOTSTRAP).
• Includes an os_is_unix() check to ensure it only runs on relevant platforms (no-op on Windows).

Testing
Created a new project (fpm new test_perms), installed it, and verified via ls -l that the resulting binary in ~/.local/bin (or prefix) has -rwxr-xr-x permissions.

test_perms [ master][?][🅵  9.4.0][🅒 lf]
❯ fpm install --prefix ./inst
 + mkdir -p build/dependencies
test_perms.f90                         done.
libtest_perms.a                        done.
main.f90                               done.
test_perms                             done.
[100%] Project compiled successfully.
 + mkdir -p ./inst/bin
# Update: build/gfortran_A86CEF2075723C1E/app/test_perms -> ./inst/bin

test_perms [ master][?][🅵  9.4.0][🅒 lf]
❯ ls -l inst/bin/test_perms
-rwxr-xr-x 1 anas anas 16912 Jan 22 17:42 inst/bin/test_perms

• Regression Testing: Ran the full test suite via fpm test. All 35 tests PASSED.

[Copilot]

Pull request overview

This PR fixes an issue where binaries installed via fpm install did not have executable permissions set, requiring users to manually run chmod +x. The fix adds a new set_executable function that uses the C chmod function for efficiency on Unix systems, with a fallback to shell commands during bootstrap, and skips the operation on Windows.

Changes:

• Added set_executable subroutine in fpm_filesystem.F90 that sets executable permissions (755) on Unix systems
• Modified install_executable in installer.f90 to call set_executable after installation
• Optimized exe_path calculation to avoid duplication for macOS rpath operations

Reviewed changes

Copilot reviewed 2 out of 2 changed files in this pull request and generated 3 comments.

File	Description
src/fpm_filesystem.F90	Adds new set_executable subroutine with C binding to chmod for non-bootstrap builds and shell fallback for bootstrap
src/fpm/installer.f90	Calls set_executable after installing executables and reuses exe_path variable for macOS rpath commands

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[Copilot]

The bootstrap fallback path silently ignores chmod failures by not checking the exitstat value. While a warning is logged in the non-bootstrap path when chmod fails, the bootstrap path should also handle failures consistently. Consider checking the stat variable and logging a warning if the command fails.

Suggested change

	call run("chmod +x " // filename, echo=.false., verbose=.false., exitstat=stat)
	call run("chmod +x " // filename, echo=.false., verbose=.false., exitstat=stat)
	if (stat /= 0) then
	write(stderr, *) "Warning: Failed to set executable permissions on: ", filename
	end if

[Copilot]

The new set_executable function lacks test coverage. Since the repository has a test_filesystem.f90 file with tests for other filesystem functions, consider adding a test to verify that executable permissions are correctly set on Unix systems and that the function is a no-op on Windows.

[Copilot]

The comment is misleading because it suggests the removed line was incorrect or unnecessary, when in reality it was moved earlier for efficiency. Consider clarifying this as "Reused from above" or simply removing the comment since the code is self-explanatory.