This patch fixes inconsistent behaviour of fish when executing absolute binaries in absolute path.

When executing command as /bin/<command>, fish first checks whether <command> is present in /bin/ or not. If it is found, then it will execute the command. But as we are using termux-exec, fish will actually try to execute <command> in @TERMUX_PREFIX@/bin/.

An example of this:-
/bin/ls:
1) Fish will first try find whether ls binary exists in /bin and whether user has permissions to execute it
2) If both the above are true, fish will try to execute /bin/ls.
3) But since we are using termux-exec, the path will be remapped to @TERMUX_PREFIX@/bin/ls
4) This is a *highly* inconsistent behaviour.

This can cause weird bugs when a script tries to execute with hardcoded paths, it might get errors about command not found even if it exists, because fish is checking it at the wrong place.

This patch has been tested to fix the bug
--- a/src/path.cpp
+++ b/src/path.cpp
@@ -42,10 +42,20 @@ static bool path_get_path_core(const wcs
     // If we let this through, we'd end up checking up to the NULL,
     // so we'd get the wrong path.
     if (cmd.find(L'\0') != wcstring::npos) return false;
+    // Map /bin and /usr/bin to @TERMUX_PREFIX@
+    wcstring _cmd;
+    
+    if (string_prefixes_string(L"/bin", cmd)) {
+      _cmd = L"@TERMUX_PREFIX@" + cmd;
+    } else if (string_prefixes_string(L"/usr/bin", cmd)) {
+      _cmd = L"@TERMUX_BASE_DIR@" + cmd;
+    } else {
+      _cmd = cmd;
+    }
     // If the command has a slash, it must be an absolute or relative path and thus we don't bother
     // looking for a matching command.
-    if (cmd.find(L'/') != wcstring::npos) {
-        std::string narrow = wcs2string(cmd);
+    if (_cmd.find(L'/') != wcstring::npos) {
+        std::string narrow = wcs2string(_cmd);
         if (access(narrow.c_str(), X_OK) != 0) {
             return false;
         }
@@ -51,7 +61,7 @@
             return false;
         }
         if (S_ISREG(buff.st_mode)) {
-            if (out_path) out_path->assign(cmd);
+            if (out_path) out_path->assign(_cmd);
             return true;
         }
         errno = EACCES;
@@ -68,7 +78,7 @@
     int err = ENOENT;
     for (auto next_path : *pathsv) {
         if (next_path.empty()) continue;
-        append_path_component(next_path, cmd);
+        append_path_component(next_path, _cmd);
         std::string narrow = wcs2string(next_path);
         if (access(narrow.c_str(), X_OK) == 0) {
             struct stat buff;
