Delete %clang and add an example about -march=armv7a

Project-Setup.md

@@ -152,12 +152,6 @@ By default `.ccls` specify compiler flags of files not listed in
 `compile_commands.json` is parsed, the rest lines of `.ccls` will be appended
 to the compiler flags.
 
-### `%clang`
-
-Resolves to either `clang` (C) or `clang++` (C++). This is useful if your
-project has both C and C++ source files, because if unconditional `clang++` is
-used instead, `clang++ a.c` parses `a.c` as C++.
-
 ### `%c` / `%cpp` / `%objective-c` / `%objective-cpp`
 
 This argument should be added only when parsing C (`%c`), C++ (`%cpp`),
@@ -168,12 +162,19 @@ Objective-C (`%objective-c`), or Objective-C++ (`%objective-c++`) files.
 This argument should be added only when indexing C header files (`%h`: `*.h`) or C++
 header files (`%hpp`: `*.hh` `*.hpp`). Note, `*.h` files are considered as C, not C++.
 
+### Compiler driver
+
+The compiler driver (the first line unless `%compile_commands.json` is used) can usually just be `clang`.
+`clang++` is usually unnecessary, and incorrect if some files are C.
+
+Note that `clang a.cc` and `clang++ a.cc` are different, but the difference is only related to linking (what default runtime libraries are passed) and is not relevant for the frontend actions ccls performs.
+
 ## `.ccls` examples
 
 #### Example A
 
 ```
-%clang
+clang
 %c -std=c11
 %cpp -std=c++2a
 %h %hpp --include=Global.h
@@ -194,7 +195,19 @@ header files (`%hpp`: `*.hh` `*.hpp`). Note, `*.h` files are considered as C, no
 -Iinc
 ```
 
-It appends flags so `%clang` should not be used.
+It appends flags so `clang` should not be used.
+
+#### Example: `-march=armv7a`
+
+See <https://github.com/MaskRay/ccls/issues/107>.
+If the compiler driver is a GCC cross-compiler, `--target=` may be required. Suppose `arm-linux-gnueabi-gcc -march=armv7a` is used, add a `--target=`:
+
+```
+%compile_commands.json
+--target=armv7a-linux-gnueabi
+```
+
+Otherwise clang will `error: unknown target CPU 'armv7a'`.
 
 ## `compile_commands.json` examples