Add method to check for C/C++ function attributes

It's fairly common on Linux and *BSD platforms to check for these
attributes existence, so it makes sense to me to have this checking
build into meson itself. Autotools also has a builtin for handling
these, and by building them in we can short circuit cases that we know
that these don't exist (MSVC).

Additionally this adds support for two common MSVC __declspec
attributes, dllimport and dllexport. This implements the declspec
version (even though GCC has an __attribute__ version that both it and
clang support), since GCC and Clang support the MSVC version as well.
Thus it seems reasonable to assume that most projects will use the
__declspec version over teh __attribute__ version.

3 files changed, 104 insertions, 0 deletions

diff --git a/docs/markdown/Reference-manual.md b/docs/markdown/Reference-manual.md
index e59c153..71771a5 100644
--- a/docs/markdown/Reference-manual.md
+++ b/docs/markdown/Reference-manual.md
@@ -1753,6 +1753,18 @@ the following methods:
 
 - `version()` returns the compiler's version number as a string.
 
+- `has_function_attribute(name)` *(added in 0.48.0)* returns `true` if the
+  compiler supports the GNU style (`__attribute__(...)`) `name`. This is
+  preferable to manual compile checks as it may be optimized for compilers that
+  do not support such attributes.
+  [This table](Reference-tables.html#gcc-attribute-support) Lists all of the
+  supported attributes.
+
+- `get_supported_function_attributes(list_of_names)` *(added in 0.48.0)
+  returns an array containing any names that are supported GCC style
+  attributes. Equivalent to `has_function_attribute` was called on each of them
+  individually.
+
 The following keyword arguments can be used:
 
 - `args` can be used to pass a list of compiler arguments that are
diff --git a/docs/markdown/Reference-tables.md b/docs/markdown/Reference-tables.md
index 46bcc3d..ab79abd 100644
--- a/docs/markdown/Reference-tables.md
+++ b/docs/markdown/Reference-tables.md
@@ -99,3 +99,66 @@ These are the parameter names for passing language specific arguments to your bu
 | Objective C++ | objcpp_args |
 | Rust          | rust_args |
 | Vala          | vala_args |
+
+
+## Function Attributes
+
+These are the parameters names that are supported using
+`compiler.has_function_attribute()` or
+`compiler.get_supported_function_attributes()`
+
+### GCC __attribute__
+
+These values are supported using the GCC style `__attribute__` annotations,
+which are supported by GCC, Clang, and other compilers.
+
+
+| Name                 |
+|----------------------|
+| alias                |
+| aligned              |
+| alloc_size           |
+| always_inline        |
+| artificial           |
+| cold                 |
+| const                |
+| constructor          |
+| constructor_priority |
+| deprecated           |
+| destructor           |
+| error                |
+| externally_visible   |
+| fallthrough          |
+| flatten              |
+| format               |
+| format_arg           |
+| gnu_inline           |
+| hot                  |
+| ifunc                |
+| malloc               |
+| noclone              |
+| noinline             |
+| nonnull              |
+| noreturn             |
+| nothrow              |
+| optimize             |
+| packed               |
+| pure                 |
+| returns_nonnull      |
+| unused               |
+| used                 |
+| visibility           |
+| warning              |
+| warn_unused_result   |
+| weak                 |
+| weakreaf             |
+
+### MSVC __declspec
+
+These values are supported using the MSVC style `__declspec` annotation,
+which are supported by MSVC, GCC, Clang, and other compilers.
+
+| Name                 |
+|----------------------|
+| dllexport            |
+| dllimport            |
diff --git a/docs/markdown/snippets/function_attributes.md b/docs/markdown/snippets/function_attributes.md
new file mode 100644
index 0000000..5514494
--- /dev/null
+++ b/docs/markdown/snippets/function_attributes.md
@@ -0,0 +1,29 @@
+## Helper methods added for checking GNU style attributes: __attribute__(...)
+
+A set of new helpers have been added to the C and C++ compiler objects for
+checking GNU style function attributes. These are not just simpler to use, they
+may be optimized to return fast on compilers that don't support these
+attributes. Currently this is true for MSVC.
+
+```meson
+cc = meson.get_compiler('c')
+if cc.has_function_attribute('aligned')
+   add_project_arguments('-DHAVE_ALIGNED', language : 'c')
+endif
+```
+
+Would replace code like:
+
+```meson
+if cc.compiles('''into foo(void) __attribute__((aligned(32)))''')
+   add_project_arguments('-DHAVE_ALIGNED', language : 'c')
+endif
+```
+
+Additionally, a multi argument version has been added:
+
+```meson
+foreach s : cc.get_supported_function_attributes(['hidden', 'alias'])
+   add_project_arguments('-DHAVE_@0@'.format(s.to_upper()), language : 'c')
+endforeach
+```